I have a Permissions Post for Kaneki here, should anyone want to contact me in concerns to playing with him (the comments are all screened), but here is a rundown of the warning posted there:

Kaneki's canon, Tokyo Ghoul, involves non-human individuals known as Ghouls that must eat people to survive. Kaneki is a half-ghoul, and as such will not be inclined to discuss anything regarding them or cannibalism with anyone beyond canon-mates, should he get any. However, I am fully aware that this is a subject that some people might find upsetting, so if you would rather not have Kaneki interact with your character at all regardless please let me know! It will be perfectly fine with me and will not upset me in any way.

Kaneki will not be retaining any of his Ghoul abilities in cosmo, and as such this will not pose a problem to him or anyone else. The most that should come up may be introspection in brackets, and potentially conversation with close CR should Kaneki find himself comfortable enough to discuss it. But, again, please let me know if you would prefer it not be brought up at all and I will ensure it isn't.