So, in thinking about the moral/ethical hierarchy of (mostly bad) actions in this story, I got to wondering:
What’s the healthiest relationship in the series?
Shouko/Asahi, right? There's nothing internally wrong with that one, relatively speaking.
I mean, aside from one of them being dead, I imagine that would makes things a little more complicated.
I take the point, though—in moral/ethical terms it’s probably as benign as it gets here. But there’s no doubt that the relationship ultimately was deleterious to Shouko’s physical health.
At least we know that the relationship is unlikely to take a darker turn, although in this series I’d never say it’s impossible for anything to get worse.
...You make a good point.
But looking at all the "possible" relationships, using that term very, very loosely, we have:
Sato/Shio (codependence, manipulation, harm to outside parties)
Shouko/Asahi (Asahi's not in a position to love someone, Shouko is currently indisposed)
Shouko/Sato (Apparently the "I love you" might have been platonic :c ...Also Sato murdered her)
Sato/Mitsuboshi (manipulation, neither party is in a good place to love someone, the confession hasn't been brought up again)
Mitsuboshi/Shio (no)
Sato/Suu (Suu is being played like a fiddle, stalking, nonmutual)
Daichi(the teacher)/Sato (stalking, cheating, manipulation, attempted statutory, nonmutual)
Daichi/his wife (he's been cheating on her for ages with minors)
Manager/Mitsuboshi (actual sexual assault, statutory, ptsd, nonmutual, kidnapping, torture)
Yuuna/her husband (the worst thing on this list somehow)
But come next chapter, maybe Mitsuboshi will meat Sato's aunt, her love of broken people will meet his fear of adult women, and we will get an even more unhealthy interaction.
Either way, out of this list, if one being dead is a disqualifier, we would have to say that the teacher and his wife have the healthiest relationship. At least she's blissfully happy.