Well, if Nika was enjoying it, he probably had no reason to be upset with Nami during this period, unless the optics changed after he ended up in the hospital. And generally this thing with this hospital is an additional thing that I don't really understand, whether it's a typing error or not, but the timeline doesn't match. They went to high school 6 hours west and he ended up in Aquilla hospital in Wollust, it was nowhere confirmed that they changed high school, how long have they lived there?
I'v written at length about that plot hole, I won't bore the thread with repeating all the ins and outs. It's bad writing. The cabin is 6 hours away from where they are by the way, not the school. The school is just "out west". But the lake is the lake that they currently go to, which was walking distance from their old house. It's eldritch geometries of time and space, strange calculus to make it work.
The important takeaways:
- the school is simply a different school from the one all the others went to (other than Nia), and the coaches of ZPR think it's close enough to track the prospects of students there.
- he got hospitalised from a violent incident, that has resulted in him losing the agressive fighting stance and attitude he had right after Summer disappeared.
- It appears they had some sort of special deal finishing school to avoid further hassle after Nika was hospitalised (maybe to do with the charge that was brought against him).
Timeline appears* to be:
- happy Summer time, all three happy yay! except Nami faking, somewhere in Wollust in Tropics highschool, starting out and Nika is almost captain of the team, he's so good yay!
- Summer went somewhere not in Wollust,maybe heaven, maybe hell
- Nika and Nami are at Tropics highschool, Nika can be arsed doing anything other than beating people up. Nami is enjoying being out of Summer's shadow even if Nika's now a proplem. This is a couple of years.
- Nika gets in a violent incident and is hospitalised, highschool is over (no idea if they finished remotely, or just didn't finish).
- Game starts, it's probably been a year after the incident. Noji wants him out being productive so she can get some of Nick instead.
*may not be true
Treat it like a dream where things are far away, but you can reach them in a single step. the distance doesn't really matter to the story other than explaining why they don't know anyon at ZPR.
Regards Nika enjoying beating people up, he can enjoy it and enjoy being mad at Nami for wanting rolls. He could have enjoyed hating her at that point, because she snitched on him to Officer Laverne. I don't think we can reduce the motives of what's going on there until we actually know, because Nika has already mentioned he's been lying to Amber when describing it. And, his memory is lying to him, he can't remember the hospital until reminded.