I'm going with Satou being the yandere seme (seme means 'the dominant one' or a more common term 'top') in the relationship. And the reason why Saiki doesn't know is that Satou doesn't really think about him being a yandere at school but at home, he's wondering who his senpai is.
VOCÊ ESTÁ LENDO
The Average Couple {Satou x Saiki}
DiversosSaiki knew about his obsession with Satou But he never thought it would come to this... This was really hard to make... ꧁𝔼𝕟𝕛𝕠𝕪꧂ ꧁Enjoy꧂