I share the sentiments of others that found Kuroko's action's in School Destruction to have been vile enough to damage my "connection" to her (as well as, IMO, out of character for her). I had to think for a bit on why that is, given the way this manga works and what we know about her. Here's how I explain it.

Up until that point, we never saw Kuroko take deliberate (as opposed to negligent) action to murder someone who wasn't a serious direct threat to her life or safety. Basically, the "big bad" of each arc, with outsized superpowers who absolutely was attempting to kill her at the same time. Under no circumstances can you say that three schoolgirls with baseball bats posed any kind of threat to Kuroko. Her role, by the "rules" of the story, is to execute those that the state is unprepared and unable to handle. No matter how awful the delinquent girls were, as terrible as what they did to Minako was, the state is capable of dealing with normal human battery and sexual abuse.

Even if she wished to mete out some measure of vigilante justice, it's hard to argue that brutal execution is the fit punishment for that crime. And, aside from the umbrella violation which was gross and unnecessary, she also is a participant in the rape of Fuuri by Minako. Even if Murcielago is an "eye for an eye" world, as someone else said, there is a particular resonance behind sexual violation that is not generally there for people watching cartoonishly gory violence. It really damages my ability to sympathize with or support Kuroko (choosing my words carefully here, because, as noted, she is not a hero or a good person even if she can behave in good ways and is the protagonist).

The fact that Kuroko's backstory is that she killed 715 people on her way to death row is largely irrelevant - it's a meaningless number thrown out to aid us in understanding early on that "this is a bad woman." We relate to the character's actions that we see, as they unfold, not to that number. A lot of the aspects of this manga are ridiculously exaggerated, to enjoy it you just have to accept that here it's possible for someone to be fifteen feet tall or a butter knife can cut bone or a 9-year-old girl can leap in the air and execute a man on a moving rollercoaster. It's why as problematic as I find Rinko and that story to be, I can grudgingly accept it by this manga's standards. I have a much harder time with the School Destruction happenings.

last edited at Apr 19, 2016 9:10PM

Much as I wish MahiMahi were actual twins (and much as I think Kishi-sensei wants the readers to basically view them that way while avoiding the letter of whatever editorial or other pressures it might have caused) the character summary page from vol. 6 calls them "擬似双子," which means "pseudo-twins."

Since there seems to be some question on it, that page also lists the class years for all the characters:

1st Years:
Mahiro
Mahiru
Yuu
Mari
Nao
Mayu　(Kaoru's kohai toy)
Mio (Ichinose)
Mariri
Midori (new character later in vol. 5)

2nd Years:
Ai
Chie
Michiru
Airi
Ayano
Miyoshi
Honoka
Alicia
Onoda (she isn't given a first name)
Yumimi
Mayuyu

3rd Years:
Kaoru
Shizuka
Nononon

last edited at Apr 18, 2016 11:26PM