Chainsaw Man Chapter 159 saw the return of the infamous "Nail Fiend" as she and Katana Man attacked Asa Mitaka and Fami inside the Tokyo Devil Detention Center. With that, fans were again left with questions surrounding the Fiend. This is because the manga has yet to confirm the Fiend's identity.
Up until now, the manga series has seen the return of several characters from Chainsaw Man Part 1, including Quanxi and Katana Man. This suggests that the Nail Fiend is also returning a character. While the manga hasn't confirmed the same, the resemblance between the Nail Fiend and Cosmo is undeniable. So, are Nail Fiend and Cosmo related?
Disclaimer: This article contains spoilers from the Chainsaw Man manga and reflects the author's opinions and speculations.
Chainsaw Man manga has yet to confirm Nail Fiend's origin
Chainsaw Man manga has yet to confirm the origin and identity of the "Nail Fiend." This suggests that manga creator Tatsuki Fujimoto might be trying to hide her identity due to plot reasons.
In most cases, if a Fiend is introduced, the manga reveals the Devil that possessed the dead body. However, that was not the case for Nail Fiend as it was only named in such a way by fans due to her powers related to nails, and the Chapter 144 title "Guns, Nails, and Katana."
Hence, there is a good chance that fans do know the Fiend from before. If one were to compare the characters that appeared before in the manga to the Fiend, the one character that comes the closest in resemblance is the Cosmos Devil Fiend - Cosmo.
Similar to the Nail Fiend's appearance in the Chainsaw Man Part 2, Cosmo's brain was also exposed in the manga's first part. This suggests that the new Fiend might be related to Cosmo. As seen in Chainsaw Man Part 1, Cosmo died at the hands of Makima as she beheaded her. Since then, the character has been completely absent in the manga.
This may lead one to believe that the new Fiend and Cosmo cannot be related. However, that's far from the truth. Fiends in Chainsaw Man are essentially devils that take over the body of dead people. Following Cosmo's death at the hands of Makima, there is a good chance that her body was left vacant by the Cosmos Devil, following which, the Nail Devil might have taken over it.
That said, this theory is merely speculation as the manga itself has revealed next to nothing about the new Fiend. Hence, fans will have to wait until manga creator Tatsuki Fujimoto reveals more about the character.
That said, some evidences deny the theory. Firstly, the Fiend's hair color is quite different from that of Cosmo. Moreover, Cosmo's right eye used to dangle from her eye socket. Meanwhile, the "Nail Fiend" did not have a right eye.
However, that's where things become interesting. Right below the Fiend's exposed brain, the manga has shown a scar around her eye socket. This suggests that her eyeball was gouged out by someone. If that is the case, there still remains the chance that the Nail Devil took over the body of Cosmo.
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