i dont think aryka even is yoen, and heres why i think so:
1.every dream aryka has had until now have always been in the first point of view, we're seeing the world through aryka who was alive in the past. his ever first dream he saw vince and yoen kissing and the two acted as if they were caught in the act.
2. In regards of people saying that aryka is yoen's brother. i dont think thats the case. because yoen's brother, as stated in chapter 26, he's weak and fragile and the parents adopted yoen to hide away the fact that their real son is weak and ill. so if you think of it, it wouldnt make sense if yoen's brother went to their school and caught them kissing. because the real son would most likely be bed ridden or hidden from the real world.
so my theory is aryka is someone (a classmate or smthn) who's a victim of bullying, we can see it in his recent dream, he seemed to have been pushed on the floor, books scattered and a bottle of water opened. and i cant seem to decipher what the blurry speech bubble said, i cant tell if its aryka's past name (hell i cant tell if these dream angels even had a past name or they're actual names were the names they had now) i also think aryka had feelings for vince in the past, an unrequited love, a very one-sided love (cause aryka knew vince had feelings for yoen [aryka's first dream]) who watched in the sidelines, i assumed that was the case because of the vince panel in aryka's dream (latest chapter) that panel looked very soft and dreamy . idk if you guys understand what i mean but it looks like a memory you would have if you have a crush on someone (idk what im talking about). also because all of aryka's dreams has always been about vince, so yeah thats where my theory came from. i also cant seem to know why aryka is an imperfect dream angel (how he feels certain emotions) its certainly weird and i think it has something to do with his past
BUT again thats just my theory, it makes no sense and i think im totally wrong i just cant wait to see what actually happened in aryka's past. or what would happen to aryka and vince if aryka got caught (i hope he doesnt)