The transformation of Tokyo Ghoul's Ken Kaneki from an accidental ghoul to a cold-hearted leader in the ghoul community suggests a similar turn to the dark side by Choujin X's Tokio Kurohara.
In Sui Ishida's Tokyo Ghoul, after being turned into a ghoul by Rize Kamishiro, shy and bookish Kaneki is appalled that he has turned into an undead being that must feed on human flesh. While he resisted giving into the consequences of his transformation, after being brutally tortured by Yamori, Kaneki not only grows to accept who he has become but leaned into it with a horrific change of personality that had him become an even worse version of the ghouls he so opposed before. This is most demonstrably illustrated in Tokyo Ghoul #75 when Kaneki hunts down and brutally tortures Ayato, in an even crueler manner than Yamori tortured him.
In Choujin X, Ishida's follow-up manga, series protagonist Tokio also exhibits several of the same attributes that Kaneki had. Like Kaneki, Tokio is a wallflower who prefers the anonymity of being one in a crowd to standing out. While the circumstances of how Kaneki and Tokio obtained their powers differ, both were never completely comfortable with the abilities that they obtained. That is, Tokio was just as aggravating as Kaneki in not embracing his power. It is also evident that their problems are connected with issues they experienced as children. However, pain is the similarity that seems most relevant in using Kaneki's sinister turn as a foreshadowing of who Tokio will eventually become. The unimaginable pain that Kaneki suffered at the hands of Yamori permanently changed him. If it weren't for the torture Kaneki might have remained the ghoul-resistant individual he had been just after transformation. This is understandable, as Yamori brought him to the edge of death, revived him, then pushed him to the edge again and again.
Pain serves a similar function in Tokio's powers. His transformation into a choujin does not simply occur with a change of clothes. Rather, he physically changes into a vulture-like creature. Naturally, that entails a degree of pain that cannot be easily gotten used to. In addition, in order to transform, Tokio must experience some traumatic experiences. So far, most of these experiences have mostly involved pain, such as falling off a building, which a normal human would have never recovered from. Like Kaneki, Tokio experiences being killed and "raised" or nearly killed Tokio and revived, over and over again. The pain of just becoming a choujin must be unbearable at the moment they occur.
In Choujin X #23, the process of changing by suffering life-threatening pain has consequences for Tokio. The more he does it, the less human he becomes. In other words, the pain is permanently changing him and decreasing his ability he has to resist his choujin self. This suggests that through the pain of transformation, Tokio, like Kaneki, will lose the humanity that has been able to balance both aspects of his personality. If this is the case, fans should not be surprised if Tokio becomes the evil Choujin X much like Kaneki's transformed into the most sinister Tokyo Ghoul.
Choujin X is available via Viz Media's website.