I made the post when i saw the spoilers so i'm more calm headed lol
I still don't know Koji's exact plan here. If Ryuen finds out he got saved by koji, he's pissed. Arisu's the same thing.
Koji likely realized the fact that Suzune is unlikely to beat him. I do feel like Koji doesn't know what to do since his plan is getting foiled though.
A weakness Koji has that I've noticed isn't his emotions but the fact that he always thinks his predictions would be accurate. If the prediction isn't accurate, he'll freak out. But he's soon or later, has destroyed his status in Horikita's class by expelling Maezono without their class consent. Ichinose now knows his true side (Koji probably did this for a reason, probably revealed in 12.5)
The only plausible theory I can think of is that both Ryuen and Arisu are so disappointed by their battle that they both drop out of the bet. (I need to reread y2v11 though)
Maybe everything has a logical consensus but tbh, the second half of Y2 has been worse than Y1 overall and the first half of Y2. I just don't know what Kiyotaka's going for here. I do agree that this is a very unpredictable volume which it's been a long time since we got one.