I'm glad someone's asking about 'Sotus' because honestly, that's such a classic Thai BL novel. The two you'll remember forever are Kongpob and Arthit. Kongpob is the first-year engineering student who gets 'hazed' by the third-year head hazer, Arthit. Their dynamic flips the typical script—Arthit has to be this tough, rule-enforcing senior with the red wristband, but Kongpob's persistent and clever refusal to be intimidated slowly cracks that shell. It’s a total enemies-to-lovers blueprint.
Most of the side characters orbit their college faculty. The other third-year hazers, like Prem and Wad, are Arthit's friend group and provide the peer pressure and commentary. Then you have Kongpob's own friend circle, like Bright and Tew, who are going through the same hazing rituals but from the freshman perspective. They're a good foil for showing how Kongpob's experience is uniquely focused on Arthit. The story really hinges on whether the strict, almost cruel system of SOTUS (Senior Order, Tradition, Unity, Spirit) can actually lead to something as vulnerable as romance between a senior and a junior.
What I find interesting, looking back, is how much the side characters' own mini-arcs reinforce the main theme. Prem's relationship with a junior, for instance, mirrors the central tension but with less resistance. It makes the world feel lived-in. The roles are pretty clearly defined by that senior-junior hierarchy, but the novel spends a lot of time blurring those lines in private moments. Arthit's internal struggle between duty and attraction is the engine of the whole thing.