[Kudryavka]

Originally Posted by Klashikari

Spoiler for Haruka's route:

Hints already indicate clearly it isn't Kanata: she was trying to hide and graffiti when Riki and Haruka were loatering around, and her flipping reaction was clearly an indication she wasn't trying to hide a mischief, but rather not want them to see that, period.
Also, you also have some conflicted response from Kanata at this point.

Kyousuke never really had the qualms to lie if it was part of his scheme. Although that theory is certainly not what I believe in the most, it is possible either.

That said, it is most likely one of the spies from the Futaki/Saigusa, considering BOTH were observed (even more confirmed in Kanata's route).

I was thinking about the graffiti, but I didn't ever realize what it said.

Spoiler for more:

It definitely wasn't Kanata, she wouldn't willingly do that and give her peers any leads onto her true backstory. But I still feel that she knew, which in no way means she is responsible. That would also explain why she got so jumpy at the blackboard graffiti, since iirc she started yelling as soon as she saw them playing on the board? Like, she yelled before she could even read it properly, else I think we would get a chance to read it too.

But yeah, despite wanting to chase Haruka away for her own good, Kanata did not cook up a plan to ruin her socially by spreading those flyers, and actually did not want it to happen.

I know I am contradicting some of what I said earlier, I'm working through the game again slowly.