Ami, Ayane, and Noriko seem severe, because they're constantly letting it show, however, I would say most of the girls in the game have things *as* severe. Miku just *shuts down screaming* at loud noises, Makoto tried to kill herself, Molly has a case of chuunibyuo to rival Rikka, on top of her lonliness/why can't the one I like see me thing, Rin.... I don't think I need to say anything for, Yumi is crushed beneath the weight of who her parents were, and thinks she's incapable of joining society, Maya is outwardly holding up super well, but you know that the weight of being the only one who remembers everything is crushing her, Tsuneyo is simply oblivious to the world to the point of her being super easily manipulated, Futaba struggles with eating disorders due to hating her body, Io so far is probably one of the milder cases, but still suffers from severe introversion, Kirin is incredibly self-destructive and potentially sociopathic, Nodoka I'm gonna go with bouts of extreme obsessiveness given the one scene where she is driven mad by not being able to figure out her literary conundrum, plus super bad insomnia, Sana is dealing with the trauma of losing her brother, and with being the shyest girl to ever shy on top of having to worry about homelessness looming and her mom going crazy from stress, Uta.... I should actually probably be worried about too. She's got her odd quirks, sure, but she hasn't really shown us what her issues are yet. Chika is dealing with abandonment issues, having to be a single parent to her little sister, and dealing with a little sister who could die if she so much as goes outside, the two girls being added in 16 to the class we've barely even seen in comparison to those above, and I have a better handle on what they're bringing to the table than Otoha and Uta.Otoha has only just begun her journey in the game, though she has been in the background for awhile. We don't yet know if her issue is even in the same category or on the same magnitude as Ami, Ayane, or Noriko...well, we at least know she's not Noriko level, there can't be that many characters in this game on THAT level of crazy, Noriko literally belongs in an asylum at this point, she's just extremely good at hiding the full extent of her issues until she's alone with player Sensei. Because of that, Otoha does not yet pose any kind of threat, but all three of the others do, or did in the past for Ayane. Strict parenting can bring A LOT of stress and I have reason to believe that will be the cause of her issue and that her issue is that she is beginning to crack under the pressure.
Anyway, I guess my point is 18 out of the 20 girls have some *serious crap* going on that we know about already (even if some of them seem to be dealing with that crap fairly well), then quirky Uta and seemingly normal lifed Otoha. I fear for these two girls, and for us.