Heads up, something reddit pointed out to me that I'd like to share here.
In the last chapter (18), Takeda has two picture frames behind his bed facing up (one that looks like it has two people close together)
However in this chapter, when Futaba is by his bed he has flipped those pictures down (and keeps them flipped down everytime she visits him afterwards)
Why would he do that? Theory is that he's a widower (lost his wife or girlfirend) those pics were of his late wife/gf, (which is why he flips them down when someone visits) and that's the reason he behaves how he does is because he doesn't want to get close to someone again (romantically).
If u read later chapters, there's some more hints supporting this theory as well (such as conversation topics and things he says offhand).