Warning: this article discusses potentially disturbing violence.
Fans who've only seen the anime adaptation of Tokyo Ghoul will be absolutely floored to learn that Ken Kaneki essentially does the same horrific thing to Touka's brother Ayato in the manga as he did to his torturer Yamori in the anime. Although a horror story with a plethora of disturbing scenes, undoubtedly the most shocking of them occurs when the evil ghoul Yamori of the Aogiri Tree extremist group tortures the hybrid ghoul/human Kaneki for nearly 10 days. Even though Kaneki eventually gains the upper hand and unleashes his own horrors upon his former assailant, it's clear due to later events in the series that the hell he endured forever changed him. But what he does next in the manga diverges greatly from what happens in the anime.
Both written by mangaka Sui Ishida, the first season of the anime Tokyo Ghoul stays mostly true to his original manga. But by the second season, also known as Tokyo Ghoul √A, Sui takes the time to tell a completely different story. In √A, Kaneki actually joins the very group that mutilated him, killing alongside the Ayato who almost murdered his own sister and Kaneki's dear friend Touka. It's safe to say that Kaneki never tortures anyone ever again in the anime. The same can't be said about the manga.
Related: Tokyo Ghoul's Nicest Hero Goes Berserk in New Manga From Series Creator
By chapter 75 in the manga, Kaneki has survived the series' most disturbing moment when Yamori tortures him, in which he eventually turned the tables on his assailant. But then he hunts down Ayato before proceeding to beat him half to death. In a manner that would have made Yamori proud had Kaneki been his student in torturing, Kaneki first
Read more on screenrant.com