Man, being in such situation is very miserable for all the people involved. Clearly the soul of the terminated-ill person is gone, only leaving the flesh behind, and yet all you can do is take care of them until the very end, while still working/studying/etc...
I was in a very similar position some years ago, so I truly respect Seiichi for taking care of his mom until the end, even with everything that happened between them.
Yall getting the fuzzies but I'm not. that look in his eyes? That's not love, that's a man ready to be done with the bullshit.
It's as if instead finishing someone off you really hate while they are wounded he's watching her bleed out so he can be satisfied he's able to see the ordeal through its end.
Either way I applaud his resolve, and I hope he finds the strength to move on.
So this is going over some of your heads. Seiichi and Seiko as shown in their cathartic flashback/memory are in a very similar headspace. Seiko has been in this headspace basically her whole life or at least since 12-14 when the neglect from her parents just built up. Seiko was not just distant but beyond desensitized emotionally and in constant dissociation, who knows what for sure but she probably has some sort of schizophrenia, or some personality disorder. Seiichi has slowly but surely been driven to this same place of dissociation and confusion for why he makes the decisions he does as he is simply trying to get by and his reactions and decisions are solely based off of his emotions in the moment. He is stimulated even less then Seiko was cause she at least had a role to play for most of the time we saw her. Now just as the relationship between Seiichi and Seiko started with a powerless individual in the care of someone who is truly disturbed it will end with a powerless individual in the care of someone who is truly disturbed.