In Tokyo Ghoul, Ghouls are flesh-eating humanoids, widely viewed as horrific monsters of the night, like blood-sucking vampires or a man-eating werewolves. Ghouls indeed have a dual nature, and some identify more with humanity than others. That includes Touka Kirishima.
Unlike the gangster Ghouls of the wards or the radical members of Aogiri Tree, Touka just wants to create a life where she can peacefully co-exist with humanity and pass herself off as human in all the ways that count. It's the legacy of her father, one that her brother Ayato isn't so keen to follow.
Touka & Ayato Kirishima, Ghoul Siblings
Touka grew up in a relatively stable and happy home, especially compared to what most other Ghouls have. She and her little brother Ayato grew up with their single father, Arata. Arata Kirishima believed in peaceful co-existence with humanity, a lesson that Touka took to heart, unlike her brother. Touka made the most of this happy life until CCG investigators found and killed Arata, before coming for his children, as well. Touka and Ayato were cornered by investigators, and Touka used her wing-like kagune for the first time in combat. From there, a serious rift formed between Touka and Ayato, with the former continuing to seek peace and the latter seeking revenge. Ayato wanted to feed his Ghoul instincts and enjoy his power, something that Touka couldn't accept. Eventually, Ayato ended up with Aogiri Tree, while Touka eked out a life for herself.
Years later, Touka found work at the café Anteiku, a neutral ground where Ghouls and human beings could co-exist and relax without any fear of violence. Run by Mr. Yoshimura, a powerful Ghoul in his own right, the elderly proprietor became a grandfatherly figure to Touka. And it wasn't just Anteiku that gave peace and meaning to Touka's life; she was also a high school senior, and she actually enjoyed school life, even if her essay-writing skills were lacking. Touka walked freely in the sunshine, she had an honest job and she had a comfortable high school career (and a good friend in her human classmate, Yoriko). This is what Arata wanted for his son and daughter all along.
Touka would soon get a new co-worker who needed the help just as badly as she did: Ken Kaneki, the one-eyed Ghoul. Around this time, Ken had suffered serious injuries after Rize's attack, and become a confused and desperate Ghoul himself. Touka might have seen herself in Ken, who had nowhere else to turn, in a situation not unlike her own past. She tried to look the other way, turning Ken away because of his indecisivness. Mr. Yoshimura felt differently, though, and accepted Ken as Touka's new co-worker. And it wasn't just that; before long, Touka was teaching Ken how to fight, as well as how to grind and pour coffee. She actually felt responsible for him, and a friendship slowly formed between them. In fact, when Yamori, Ayato and Nico arrived at Anteiku to kidnap Ken, Touka risked her very life to confront Yamori and her estranged brother. But despite her best efforts, Ken was abducted. Touka vowed to get him back no matter what. She couldn't lose any more family.
After Ken is rescued from the clutches of Aogiri Tree, Touka is told that he won't be returning to Anteiku, and will instead look into the mysteries of that organization and the schemes of Dr. Kano. Touka, however, had worked hard to build her peaceful life, and she belonged at Anteiku and school, not the streets. True, she had risked her life to save Ken from Shu Tsukiyama, the Gourmet, and Hinami from the brutal CCG investigator Kureo Mado, but that wasn't the life for her. Instead, Touka was content to melt into the background, throwing herself into school and studies even more, making every effort to bury her Ghoul nature and the grim reality of life in Tokyo for her people. By the time Ken sees her again, Touka is preparing to graduate high school and is scouting universities, including Ken's. She tours the campus and decides to major in biology, so she might study the true nature of humans and Ghouls, and possibly find a way to reconcile the two. Around this time, Touka runs into Ken again, whose indecisive and lonely outlook continues to irritate her. Ken's unsure whether Anteiku can do him any good. Insulted by this, Touka tells him to not return, since evidently, Ken doesn't share Touka's optimistic view on what Anteiku stands for and what it can do for Ghouls.
For now, there is a rift between Touka and Ken, just like the gulf between her and her little brother. But in time, perhaps Touka will find a friend in Ken once again. She believes in a better future, and despite her attitude, she isn't ready to give up on anyone, Ghoul or human.