Kaneki considers Touka’s transformation to be a positive thing. He is aware that he is part of the Ghoul’s World, and to fulfil his goals he knows that he will have to go deeper into it. So when Touka offered to go with him, potentially undoing all her development in the direction of the Human World, Kaneki felt like he had to refuse, to protect Touka from herself, even while it pained both him and her to do so.
Kaneki wants Touka to live like a human, because it’s the life he himself wants, but feels he cannot have. His martyr complex demands that he must shoulder the burdens of everyone else so that they can live happy lives while he alone suffers. But it’s precisely because of this complex that Touka suffers in the first place since she only wants to be by his side. In trying to be ‘save’ Touka, he only ends up hurting her.
And himself too. His own Human emotions, and the truth, nag in his head to give up his warped sense of responsibility and to go down and see her, but he shuts them out by allowing himself to be distracted by his ‘Ghoul business’.
He knows in his heart that Touka can never be a complete Human with her Ghoulish past, but won’t accept that truth. Just as he will not accept that he can never be a complete Ghoul with his Humane past.
Seriously, if any of the characters consistently listened to Yoshimura then this series wouldn’t be a tragedy, it would be a peaceful coffee shop AU. GO BACK TO ANTEIKU, KANEKI. What Anteiku represents is spiritual Half-Ghouldom - Ghouls living alongside Humans and being both monster and man, living in peace when they can and fighting when they must; a world away from the constant fighting that Kaneki’s Group undergoes and from the impotent passivity of the life of a college student. This revelation comes immediately after Yoshimura reveals that he is the father of a half-Ghoul, and it’s not just Eto - it’s the community he founded. Kaneki still doesn’t understand that, as a half-Ghoul, this is his home, where he can be both Kuroneki and Shironeki.
You’re a Half-Ghoul in body, Kaneki, so be a Half-Ghoul in spirit too.
Touka on Kaneki’s Transformation
Touka sees Kaneki’s slide completely into the Ghoul’s World as extremely negative, as he casts aside the very qualities that inspired her to change in the first place. It’s a trend she’s seen before. with both Ayato and herself, and she wants none of it.
This ‘endless bullshit’ is exactly what Ayato is doing now in Aogiri, and exactly what she did in her past hunting doves. To see Kaneki repeating her mistakes is infuriating for her.
The Bridge to Half-Ghouldom
The scene on the bridge is pivotal to our protagonists’ position on the Human-Ghoul spectrum - it’s hard to find a more symbolic setting than a bridge, after all. On one side of that bridge is the road back to the Ghoul’s World, and the other leads back to the Human’s World. Kaneki and Touka meet in the middle, and although they both leave the same way they came, the encounter with the traveller from the opposite road changes their perspectives forever.
It’s this retort from Touka that really snaps Kaneki out of his hero act. He begins to realise that if he keeps going far, far down the rabbit hole into the Ghoul Wonderland, Anteiku may not accept him back at all. He might lose his home - and it frightens him, because he realises the world of the half-ghoul is his home, not dark back alleys brawling with Aogiri.
And then Touka proceeds to demonstrate why she still belongs at Anteiku.
Kaneki’s efforts to “humanify” Touka were a complete waste of time. Touka doesn’t want the complete powerlessness that comes with living in the Human World. She wants the love and affection that it provides, but what’s that even worth, when the one she wants it from most is a denizen of the Ghoul World who refuses to give it to her? Against her better sense, she proves here that the Ghoul inside her is still alive and well. That’s why she still belongs at Anteiku - in spirit, she’s become part Human, but she’s still part Ghoul. She fits better into Anteiku’s hybrid world than the current Kaneki does.
Kaneki, seeing the Ghoul still within Touka, gives up trying to cut off part of his own nature.
And accepts that Human part of him while staying true to his new self as well, going back to Anteiku but changing his role.
Meanwhile Touka’s old self has been brought to her awareness, even if she’s still viewing it as a relapse rather than an indisputable part of herself, not realising that it was the Ghoul part of herself that she has been repressing that was what convinced him to return.
Both come close to Half-Ghouldom and the reconciliation of their fractured sense of self…
But, as is typical in tragedy, the revelation comes too late, and when the push comes to the greatest shove they remain in their separate worlds as the symbol of the worlds’ union goes up in flames, destroyed by the CCG, who want to keep those worlds separate for good.
Kaneki sticks to the ‘Ghoul’ way, and this is his punishment:
Touka wants to go down the Ghoul’s way again, but the memory of Mado’s wedding ring, one of the major stimuli for her journey into the Human World, paralyses her. She cannot escape the ‘Human’s Way’, and it’s deeply painful for her. And this is her punishment:
But despite all that, she keeps faith. She believes Kaneki will find a way back to that Half-Ghoul paradise, and sub-textually, herself as well.
But Anteiku, named after the antique coffee cup that Yoshimura saved to drink with his half-ghoul child - making the shop a beacon for the half-ghoul spirit - has been destroyed. So where does hope lie now for the hybrid existence?