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The Petrification Device ( (せき) () (そう) () Sekika Souchi), also known as the Petrification Weapon ( (せき) () () () Sekika Buki), or the Medusa (石化武器 (メデューサ) Medyūsa), are highly-advanced devices that can induce petrification.

The devices' arrival on Earth directly caused the collapse of society through the petrification of the human species. Thousands of years later, just a few centuries prior to the story's events, a large number of additional devices rained down from the skies above Treasure Island, prompting its inhabitants to abuse their power.

The South America Arc later unveiled that the initial world petrification event involved countless devices, enough to form a colossal pyramid at ground zero[1]. By the end of the series, it was revealed that the devices are sentient, mechanical lifeforms responsible for the Why-man phenomena.[2]


A Medusa is a small device in the shape of a trefoil knot with only one side, similar to a möbius strip. It appears to be approximately 6cm (2.5 inches) across at the widest points.

Senku holding medusa

Senku holding the petrification device.

Senku notes several things about its form:[3]

  • Smooth surface.
  • Circuitry inside.
  • Translucent with photosphere.
  • Twisted shape like Möbius strip.
  • About a particular element of the device:
    • Resembles LED light in form.
    • Big range of light output.
Battery Replacement

Replacing a Medusa's battery.

The device's smooth casing houses remarkably advanced circuitry of alien design, the etchings of which can be seen from the outside. Joel notes the components may be mineral-based and are of such complexity that they appear 3D-printed[4]. A carved diamond, sole recognizable component, can be found at the core of the circuitry where everything connects. The diamond acts as battery for the devices, and will slowly blacken with usage, requiring a replacement.[5]

To be usable as batteries, diamonds need to be cut in a specific shape, be free of any fractures,[6] and have central cleavage planes intersecting at the tip, presumably used to "channel something". These planes will also cause the diamonds to split perfectly down the middle if struck with precision tools[7]. Devices equipped with a defective battery will not be able to power on.

By the end of the story, it was revealed that the circuitry's complexity allows each device to think, respond, and act on its own, imbuing them with artificial intelligence.[2] It also absorbs parts of the electromagnetic spectrum, causing the Medusa to be invisible to RADAR,[8] and granting them some form of sight[9]. Similarly, they can manipulate and send out radio waves, allowing them to communicate.[10]

Medusa Stand Down

A Medusa requesting another to stand down.

Their ability to interact with the world is not limited to electromagnetism. The devices can petrify specific lifeforms or any biological byproduct by targeting DNA, as well as fly around as they see fit by ignoring gravity, both of which are achieved through manipulation of the Higgs field.[11]

While the devices can act in unison, coordinating with the rest of their species for various tasks, individual personalities and conflicting opinions were observed. One such example is seen when a Medusa readies itself to unleash the petrification, only to be interrupted by another specimen who wishes to let Senku speak.[2] Due to their properties, their goals, and their abilities, Xeno identifies them as mechanical parasites.[12]

Why-man on Emotions

Why-man lamenting the burden of emotional intelligence.

As a complex lifeform, and in spite of its mechanical nature, the Medusa is capable of perceiving, understanding, and experiencing emotional responses.[13]

This ability can be, and is disabled most of the time, however. As their mechanical design grants them immortality, emotional intelligence was considered too high a burden and was left optional.[14] In their "emotionally offline" state, the devices show no understanding of emotional processes, speak in an awkward manner, and ignore emotional impact when taking action.[15]

Despite their immortality, the devices can be destroyed.[16] Their circuitry is also vulnerable to oxidization, rendering them unconscious when entering Earth's atmosphere, and slowly killing them over time[17].


Medusa light

The Medusa's petri-beam.

Due to their nature as sentient beings, the Medusa can petrify biological species at will by targeting specific DNA,[18] provided they are conscious. In a pressurized atmosphere, humans can also unleash the 'petri-beam' on other humans by issuing voice commands.

Users must specify the beam's radius of effect, followed by the time-to-activation.[19] The radius of effect should be set in meters (allowing for decimals), and the time-to-activation in seconds or minutes (whether other units can be used is unconfirmed). Voice commands must be issued fully, from close range, and in English: being interrupted mid-speech,[20] shouting from afar,[21] or speaking any other language will not result in activation.

Successful usage of the device can be achieved through any means, so long as a valid voice command is given. This includes using microphones and speakers to activate it remotely,[22] or synthesizing speech (as demonstrated by Why-man cloning Senku's voice).[23]

Medusa activating

The medusa activating and making a noise.

Upon activating, the device hovers and begins to glow as the machinery lets out a click-like noise. Shortly after, the beam, a sphere of light visible only to the target species,[24] begins expanding outward at a constant speed,[25] passing through any obstacle[26] until its radius reaches the size defined by the voice command. During this process, any target lifeform "touched" by the beam will immediately begin undergoing petrification.

The petrification process can be stopped in two ways: by applying nital on an affected body part while petrification is still ongoing,[27] or, if only part of the body is exposed to the beam, by "discarding" affected body parts, which will stop the chain reaction from spreading.[28] As the beam's speed is limited (relative to the radius), and may be slow enough, petrification can also be avoided by getting out of range in time.[26]

Due to their ease of use, the devices were commonly used as weapons during human conflicts. The risks they carry prompted fighters to tie them to the end of spears, or use them as throwing weapons by tying them at the end of a string.[29] Due to their limited energy source, it is possible to drain the devices through overuse, even more so when targeting wide areas.[30] Insufficient available battery will result in no activation, or the beam not reaching its designated radius.[31]

The devices may also be useful if available in large numbers, regardless of their ability to petrify. As they do not show up on RADAR, it was possible to construct a futuristic stealth ship by coating the hull with many of the countless devices that originally fell on Earth.[16]



Medusa falling from the sky

The petrification devices falling from the sky over Treasure Island centuries ago.

Matsukaze tells the Kingdom of Science what happened during his time a few centuries back. A great number of petrification devices rained down from the sky above the island.[32] Either from hearing the voice that seemed to accompany the devices or from trial and error, the inhabitants of Treasure Island figured out how to use them. Matsukaze's master realized that if the devices were allowed to be wielded, chaos would reign. As such, he ordered his men to find and destroy them.

Amaryllis and her four friends being petrified

The petrification device being used on a younger Amaryllis and her friends.

With only one remaining, Matsukaze's master lay dying from a fatal injury, questioning why many were sent rather than only one big one. Matsukaze is petrified shortly afterwards, stating that only one device remains despite several being shown in the background. The image he carves onto himself does not appear to match the shown medusas very well, however he vows to tell future generations of their danger.[29] This final device is presumably the one Ibara uses later.

Later, in the year 5736, five years prior to Senku arriving on the island, the petrification device was used by Kirisame and Moz against Amaryllis and her four friends to prevent them from fleeing the island.[28]

Treasure Island Arc[]

In the year 5741, Kirisame continued to use this as a weapon. When the Kingdom of Science arrived with the Perseus on the shores of Treasure Island, Kirisame used it to petrify the majority of the crew, with the exception of Senku, Gen, Soyuz and Kohaku who were exploring, Suika who got kicked away by Ryusui and Ginro who was swimming at the time.[33]

Kirisame throwing the medusa

Kirisame throwing the medusa at Ginro and Kohaku.

Ibara later orders Kirisame to use it again against Kohaku and Ginro after Kohaku started yelling about the truth of the state of the master of the Petrification Kingdom to try and shut her up. Kohaku's goal was trying to get Kirisame to use the device on her and Ginro, who got fatally stabbed, to save him. The inhabitants are also asked to shield their eyes "or else be turned to stone", presumably a measure to hide the existence of the device from them[34]

Under Ibara's orders, Kirisame throws a fake petrification device during the first battle at Wavebreak Cliff to test Mozu's loyalty. Ibara kept the real device for himself, escaping to the Perseus.[35]

Medusa immediately after activation

The device immediately after activation.

Ibara then asks Oarashi to run the device to the center of the island, hoping to petrify all of the remaining invaders in one go. Kirisame argues with him, saying that not all of the islanders have finished evacuating yet and that the master told her that the device was never meant to be used over a large area. Realizing Kirisame is no longer on his side, Ibara petrifies her. Yo then shoots his hand, causing him to drop it into the ocean.[36]

Yo retrieves the device from the ocean but doesn't know how to use it. Ibara jumps in after him and activates it while Yo was holding it, petrifying him.[37] Oarashi dives overboard as well, and Ibara takes the opportunity to use him to petrify the whole island. He sets it for fifteen minutes, allowing Oarashi enough time to get to the middle of the island. The team realizes what's happened and Taiju tells everyone that Oarashi has the device and that he needs to be stopped. The islanders, confused as they don't know about the device, think that they need to protect him instead. It's revealed that Ibara forced Oarashi to swallow it, and with no means to stop it in time, the island gets petrified.[25]

Medusa immediately after use

The medusa after being used in Yo's hands

Ibara smashes Oarashi's body to retrieve the device from his stomach. He then finds the mobile lab, wherein Senku tries to use a microphone to activate it.[38] The speaker is too far away for it to work, however Ibara throws it away from himself regardless. Senku snatches it up and tries to petrify Ibara, but his command is interrupted and thus doesn't activate it. Ibara grabs it back and chases Senku to Wavebreak Cliff, where he attempts to use it against Senku once more. Ryusui, freshly revived, uses the drone to snag it midair.[20] A tug-of-war happens between the two sides, resulting in the device petrifying Ryusui as he attaches the earpiece. Senku then immediately afterward petrified Ibara after using the speaker.[22]

Why-man then attempts to set the device off at a radius of 12,800,000 meters (the diameter of the Earth) using the radio, but fails.[23]

New America City Arc[]

Once depetrified, Matsukaze revealed that during his time, several petrification devices fell from the sky all across the island.[32]

After returning to Ishigami Village, Senku reports that the weapon is almost depleted of power, as the last time he used it the radius did not reach the correct maximum and fell short. He uses the device's remaining power, which just barely flickers, to petrify Tsukasa and save his life.[31]

On the way to America, Matsukaze continues his story of the petrification weapons. He says that he's unsure how the people managed to figure out how they work, only that they started using them soon after. Him and his master found and destroyed almost all of them, bar one.[29]

Medusa falling into the river

The device falling into the river after Stanley shoots it.

Finding out that Dr. Xeno is their opponent, Senku realizes he can pretend to have super science weapons to trick Xeno into surrendering, as long as they don't reveal that it's out of power.[39] Ukyo later delivers it to the American Colony's front door via arrow. Xeno sees it and realizes it's hyper-tech, leaving Gen to explain what it is and bluff that the Kingdom have more of them. Stanley decides he's not particularly scared of that fact, as they have a submarine they can use to take over the Perseus before anyone can activate the device.[40]

With Xeno captured, Stanley ties the petrification device to the prow of the ship. The members remaining on the captured Perseus pretend to be scared, causing enough of a diversion to allow the smaller ship to escape. Before it passes, however, Stanley shoots it several times, launching it high into the air above the ship.[41]

South America Arc[]

Sometime later, Homura Momiji free dives into the river, retrieving the device that sunk to the bottom. Bringing it to the American Colony, Nikki then discusses tinkering with the device so it can be used for healing any injured or sick people in the future. Internally, Nikki is aware Senku has a use for the device and cannot let the truth slip. Brody agrees, but thinks the timing of the request is suspicious and insists any fiddling they do with it is monitored. It's revealed that the members of the Kingdom of Science left in North America don't know they're heading for the source, hoping to find the original device. As they are unfamiliar with performing a proper diagnosis, they revived watchmaker Joel. Getting to work, Joel notes several things about the weapon: Joel was fascinated by its mechanics and described the circuitry is glass or mineral-like, and the core is a diamond.

Petrification Pyramid

The pyramid of petrification.

Theorizing a way to get it functioning, he removes and reinstalls the diamond. Wanting to confirm it, Joel tests it on himself and gets petrified in the process.[4]

After a long trek through the Amazon rainforest, Senku and his allies discover a huge stepped pyramid of the devices.[1]

Once the diamond was re-created, Joel said the device was functional. At that point Dr. Brody and his soldiers immediately confiscated the device having become suspicious of the intentions of the Kingdom of Science. This resulted in a brawl for the device. Despite Dr. Brody's attempt to lock the device away, Joel was still able to activate it using Why-man's regularly timed broadcast, triggering the second global scale Petrification Event.

New Stone World Arc[]

7 years later, the members of the Kingdom of Science were finally revived, thanks in large part to Suika's efforts. Even Hyoga, who was stated by Tsukasa to have lost his life prior to the petrification, was successfully brought back. Tsukasa relayed this information to Senku, and through this, the latter's hypothesis was confirmed. That it's possible for the petrification device to even nullify death. With this, humanity has secured a means of immortality.[42]

Globetrotting Arc[]

Ukyo and Yo by reunite with the Perseus crew and they bring with them the working Petrification Device. It is then revealed that the devices from South America are duds, potentially too old to function, since Kaseki's diamond batteries work fine with the device from Treasure Island.[43]

Moon Mission Arc[]

Knowing that the petrification devices can deteriorate over time Senku and Kaseki enclose the only working device in a vacuum sealed container in order to preserve it. The device later begins to rattle and activates while in the vault it's kept, petrifying Gen and Yo in the process.[44] This incident spurs a lot of theories as to what might have triggered the device, but eventually Senku decides it's too risky to experiment on it to reproduce that occurrence so its battery is removed and its vaulted again, this time with cameras monitoring it.[45]

When the time for the rocket launch arrives, Kaseki and Joel re-activate the working device by inserting a diamond battery in it.[46] It is subsequently used to petrify the astronauts until the rocket safely leaves the Earth's atmosphere, from which point on they are revived by the 'resurrection watches' that Joel had crafted for the occasion.[47]


The only remaining petrification device

The vacuum capsule hosts a new petrification device.

The sole device that chose to stay behind with humanity as it deemed Senku's proposal during the Why-man negotiations to be interesting, despite its near-zero chances of success. It offers itself as a living specimen and states that it's fine with potentially being killed or destroyed. It is enclosed in the same container the Medusa from Treasure Island was housed prior, with the addition of two lines and an 'x' one of the astronauts drew on it, which functions as a face and makes it look more palpable to human sensibilities. It is very inquisitive and talkative and it eagerly answers most questions Kohaku has, while also voicing several questions of its own. It particularly questions humanity's rejection of the petrification and immortality, as that remains a concept that puzzles it deeply, even after its explained.[9]

Senku's whyman purse

Why-man hanging out.

When Gen returns to Japan for Yuzuriha's wedding a few years later, it is seen again strapped around Senku's lab coat. The capsule that contains it also has a little rope made by Suika tied on it,[48] similar to a keychain, denoting its status as an Ishigami Villager. When Senku reveals the plan to make a time machine, it claims that its own investment on it is the prevention of the multiple deaths of its kind.[11]

The device has not revealed any name for itself or its species, however Gen[11] and later Chrome[49] refer to it as 'Why-man' while 'medusa' is used when referring to its species.


  • One of the nicknames for the device, the Medusa, is a reference to one of the Gorgons from Greek mythology.
  • In the anime, the device's model is not a Möbius strip and has two sides.
  • The device has a finite amount of power, another nod to the formula E=MC2.
  • The largest known radius specified as target was 12,800,000 meters, the diameter of the Earth.
  • It was mentioned a voice was heard with the devices falling, it was revealed much later that this voice emanated from the devices themselves in the form of radio waves, which were powerful enough to be heard by the inhabitants of Treasure Island through some fortuitous mechanism involving their headpieces behaving like antennas.[50]
    • Although the explanation for how the islanders heard the radio waves is quite fantastical, there are numerous real world anecdotes about radio waves being picked up and turned into sound by random objects, most famously teeth fillings and braces (although doubt has been cast on whether teeth fillings can actually do this), but also cases such as cutlery sitting on top of a silverware tray. These anecdotes date mostly from the mid 20th century when very powerful AM radio transmitters were in use, and were usually localized within the immediate vicinity of such transmitters.
  • Matsukaze said that they were able to destroy the devices, however Stanley is shown shooting it several times, making it unclear how durable the devices are and how difficult they are to break.[41]


  1. 1.0 1.1 Dr. Stone Manga: Chapter 180
  2. 2.0 2.1 2.2 Dr. Stone Manga: Chapter 228
  3. Dr. Stone Manga: Chapter 139, Page 5
  4. 4.0 4.1 Dr. Stone Manga: Chapter 177
  5. Dr. Stone Manga: Chapter 182, Page 3
  6. Dr. Stone Manga: Chapter 182, Page 7
  7. Dr. Stone Manga: Chapter 185, Page 8
  8. Dr. Stone Manga: Chapter 181, Page 17
  9. 9.0 9.1 Dr. Stone Manga: Chapter 231
  10. Dr. Stone Manga: Chapter 228, Page 5
  11. 11.0 11.1 11.2 Dr. Stone Manga: Chapter 232
  12. Dr. Stone Manga: Chapter 228, Page 19
  13. Dr. Stone: 4D Science Chapter 3, Page 32
  14. Dr. Stone: 4D Science Chapter 3, Page 33
  15. Dr. Stone: 4D Science Chapter 1
  16. 16.0 16.1 Dr. Stone Manga: Chapter 181
  17. Dr. Stone Manga: Chapter 230
  18. Dr. Stone Manga: Chapter 229, Page 4
  19. Dr. Stone Manga: Chapter 134, Page 5
  20. 20.0 20.1 Dr. Stone Manga: Chapter 136
  21. Dr. Stone Manga: Chapter 191, Page 2
  22. 22.0 22.1 Dr. Stone Manga: Chapter 137
  23. 23.0 23.1 Dr. Stone Manga: Chapter 138
  24. Dr. Stone Manga: Chapter 229, Page 5
  25. 25.0 25.1 Dr. Stone Manga: Chapter 133
  26. 26.0 26.1 Dr. Stone Manga: Chapter 108
  27. Dr. Stone Manga: Chapter 135
  28. 28.0 28.1 Dr. Stone Manga: Chapter 106
  29. 29.0 29.1 29.2 Dr. Stone Manga: Chapter 146
  30. Dr. Stone: 4D Science Chapter 2
  31. 31.0 31.1 Dr. Stone Manga: Chapter 141
  32. 32.0 32.1 Dr. Stone Manga: Chapter 139
  33. Dr. Stone Manga: Chapter 103
  34. Dr. Stone Manga: Chapter 121
  35. Dr. Stone Manga: Chapter 127
  36. Dr. Stone Manga: Chapter 131
  37. Dr. Stone Manga: Chapter 132
  38. Dr. Stone Manga: Chapter 134
  39. Dr. Stone Manga: Chapter 158
  40. Dr. Stone Manga: Chapter 161
  41. 41.0 41.1 Dr. Stone Manga: Chapter 169
  42. Dr. Stone Manga: Chapter 197
  43. Dr. Stone Manga: Chapter 209
  44. Dr. Stone Manga: Chapter 213
  45. Dr. Stone Manga: Chapter 214
  46. Dr. Stone Manga: Chapter 223
  47. Dr. Stone Manga: Chapter 220
  48. https://youtu.be/lXt5HHKcpgg?t=247
  49. Dr. Stone: Terraforming, Page 11
  50. Dr. Stone Manga: Chapter 146, Page 7

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