Ah, thanks so much for responding! I would absolutely love to see what your version of a Tei-like character would be like! I've also still been searching for more like him. I think he's the only character I kept wanting to jump ship for in the other routes (I know some people were annoyed how he showed up in the other routes, but I was always like, yes, please, I would totally switch LIs if not for needing to actually finish the game, haha).
For BTD2, it's been a while but I think I preferred Vincent and Cain (Lawrence is interesting in an eerie kind of way, and Ren is...more of a masochist iirc?). Cain's route also has an extra hidden character mini route who is kinda similar to him.
I haven't played Black Wolves Saga yet either. It's a little more involved since the English is a fan translation as far as I'm aware, and I've just been too lazy so far to go through the extra steps to set it all up. Nightshade's yandere is in my opinion a touch underwhelming. Don't get me wrong, he definitely has some possessiveness/obsessiveness come through, but I found his route...not extreme enough for me, haha. The voice actor is fantastic, though, and does such a great job with the emotional lines. Not sure if you want to be spoiled as to which character (SPOILER: his name is Kuroyuki, what a coincidence!)
Anyway, hope you're staying safe and well, too! I'll post again if I remember/find any others (although a lot of the recent games I've seen mentioned are only on PS Vita which I don't have unfortunately), always nice to find fellow male yandere fans!