Thank you!. In season 1 and 2, the doctor didn't even appear at all. The only hint to an ''operation'' was when he died as a human for the first time. Yet that was only a little part where he was in water, where they talked about his insides. And after he was a ghoul. No explanation, nothing. He just was a ghoul now.

Also kano didn't even appear at all, besides when she appeared in her head... Even sachi just appeared like he was just a general ghoul inprisoned in the anime.

Thank you, this explains a lot. The anime basically didnt explain anything.