I have this headcanon that Saino was just lucky to have been pursuing girls that just so happened to be fond or optimistic towards him.
Sensei has a pure heart and is inclined to believe his antics. Natsuno may have a crush on Saino, with Akitsu having an interest towards him as Natsuno's wingman.
For this case.. Yurushima seems cold but is likely caring for those who gather the courage to interact with her. She was so dedicated at teaching Saino that she had been tutoring him way past class hours. Plus, she straight-up drank the entire bottle without double-checking just because he said "the vending machine ['s refrigeration] is broken". She definitely would've noticed the tiny hole at the side of the bottle, with it likely leaving a teeny tiny bump from where the tough plastic was punctured.
It's true that Saino is the sleazy yet clumsy mastermind initiating all these coercion and mind-control attempts to have s*x with these women... but their personalities and reactions were also written in such a way that he's getting lucky most of the time.
Well... not a problem for me. I feel sorry for all the brainwashing but I wanna see how it all plays out. More s*x? Saino being found out? Drama? Harems? Character development? Just more s*x.
