None of those notes about Seo really sounded bad enough to kill someone over? The two that were covered might be, but you can't really read them. I would have put "Seo killed my cat and laughed" front and center if I was trying to convince people Seo was a bad enough bully to deserve to die.

The way the letters are worded seems that people just assumed she did those things or at least that's how it is in the unofficial English translation. Seo was really mean to Satsuki but who knows if the accusations were true or if they were exaggerated.

AHAHAHAHA, really got us with that one. Damn... for like only a page I truly did start believing this was going to end happily.

Goodbye Natsuki for real this time, and now that Tokiko has nothing left. Let's see how this tragedy ends

she will just go and catch a train to go someplace far away

I'm a little confused, so Aoya killed the schoolteacher and the shirokis, and "adopted" Ai 2 years ago? And recently he killed Rina. Saying he was going to kill Tokiko last implies he's killed more, but all the other deaths around Tokiko are incredibly convoluted and hard to pull off. Also does this mean the thing the dead detective worked out was that it was Aoya or something else?

Not every death is a murder.

^ we did see the corpse tho. Admittedly, I don’t think it looked much like her and suspect that she’s actually still alive myself, but the corpse Tokiko identified as Rina was shown to the audience back in ch. 9

I read the whole manga and she's dead along with every Kurosu.
Don't expect any yuri or happy ending though. The ball was death's last fuck you to Tokiko before she did what she thought she had to do.