Chapter 17. I wanna say "what a ride" but this isn't over. The angst isn't over. Legit scares me tbh.
If Aya has become a kind of monster then I say let her be the bigger, meaner, faster one, cuz it might mean confronting and shaking up Sei to her core, like Aya's Eren or something, and doesn't wait for Sei to become her final form and just punches Sei in the face. Aya has the potential to be an attack titan then.
Sei, perhaps without meaning to, has successfully passed the poison to her student/lover (yikes). Jesus, come to think of it, education is largely about the transfer of knowledge, skills, and sometimes societal/cultural baggage. In this case, Sei has transferred the "baggage" of being a horrible psychological shitshow to Aya.
The difference, I think, is of all the characters here (I am excluding the male sensei, just focusing on the more relevant ones in the darker sphere), Aya is the only person with remaining moral semblance. Initially, I would have given this to Haruki, but her main motivation is to control Aya in the guise of freeing her from a perverted teacher... Is it love tho? Maybe. But if Aya hadn't controlled the reins in this chapter, Haruki would have succeeded in consuming Aya, not exactly a loving one. Haruki would have kept Aya in obsession, the way Sei has kept Yoru.
Aya's main motivation for sticking with Sei's world of hell is because of Love, as cheesy as it sounds, that's how I look at it, plus she has fended off Haruki's advancements on her in a reverse-psychology way. If she's as a twisted fuck as her gf, Aya would have destroyed her friend. She might become the "Yoru" to Haruki's "Sei".
Aya wanting to free Sei from Yoru is different from Haruki's kind of love. Aya wants to unburden Sei of Yoru so they can set things right for real. The "Yoru Obsession" is what makes Sei so desperate that she sleeps with whoever not to mention she toys with students which could land her in fucking jail.
BUUUT Chapter 17 seems like an unraveling. I am sensing a subversion of my expectations so strong it could slap me in the face with a 14-inch dildo of twists and turns. I am hoping Aya won't become Sei's carbon copy. Just become the meaner one, please. Been rooting for Aya to propel things in their right direction...