Warning! Spoilers ahead for Choujin X chapter 21!
Why Ken Kaneki's kagune manifests as a centipede (especially when he becomes a kakuja) in mangaka Sui Ishida's Tokyo Ghoul is similar to why the Beast Chouin Tokio Kurohara's Beastification takes the form of a vulture in Ishida's new manga Choujin X.
In his earlier and critically acclaimed manga series Tokyo Ghoul, one of the most defining features that Ishida gave his eponymous monsters was the predatory organ known as the kagune. But rather than making them even more special than they already were by explaining why certain kagune took certain forms in relation to the user, he severely limited kagune to only four types (essentially based on what part of the body they grew out of). The main exception was, of course, Kaneki who eventually grew a centipede-esque kagune, in addition to the one he obtained from the ghoul Rize, after Tokyo Ghoul's Aogiri Tree member Yamori tortured him with such an insect.
Related: Choujin X Broke its Hero With a Grotesque Death Too R-Rated For Anime
In Choujin X, however, Ishida is clearly expanding upon the inherent complexities of Kaneki's centipede kagune with Tokio's Beastification form — and possibly Azuma Higashi's own, though his latest transformation in chapter 21 seems to contradict this. Earlier chapters of Choujin X explain why Tokio turns into a vulture-like creature. As a kid, his classmates referred to him as a buzzard because of how he would always hang around and benefit from his friendship with the highly popular Azuma whose status as a minor superhero led to some exciting encounters. Even Tokio's power as a Choujin seems to stem from that friendship's dynamic. Recent chapters also heavily implied that Azuma's own Choujin
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