I have the same tastes as you, I love oblivious mc in mystery settings, and type B with blackmail/rape + corruption over time, especially if the girl has some personality/is feisty/strong willed.
What games did you play?
Honestly, hard to list them all. Few of them really always fit the bill, that is the issue. Most success you will have with non-NTR or non-NTR-focus corruption games with female knights or warriors or smth like that. Some of them have side characters who fit the bill too. Anyway, Im going to list some that come to mind that have at least a few of the mentioned criteria:
- Scars of Summer /Summer Shattering (NTR, childhood friend, tomboy, but big boobs)
- The Cruse of Kubel / Kubel's (Choker) Disease (childhood friend, powerful mage, blackmail/coercion, rape (one time, first scene), but shes a bit girly)
- Nebel Geisterjäger (a bit too unceremonious for me in how the thing starts, build-up isn't that great and it lacks out-of-h-scene dialogue and interactions that really drive home the point of the NTR)
- Henteria Chronicles Chapter 2 (pixel-art, Step-sibiling, strong but has a crush on MC, a few side characters with different kink themes) (sequel (Chapter 3) has a few good characters too, but its in development. it has a demo every few months though, so check it out)
- Tiina, Swordswoman of Scarlet Prison (not NTR, but strong female character, red hair, with corruption elements)
- Kuro Reina's Gaiden/ Dark Beauty Reina Extra Story (only the extra story) (has a side character arc with 4-5 scenes revolving around a guard captain being blackmailed by a disgruntled former captainl, no NTR tho)
- 刻まれた快感 - which is basically like Kubel's Curse (same artist, different writer) (small game, but some neat stuff. still, FMC isnt really a tomboy or strong-willed, that is the issue)
- 神桜姫~勝気クールな爆乳姫巫女は権力者のマゾ雌オナホ嫁に寝取られ - (honestly, kind of a cheap ass game from a gameplay perspective imo (even for an RPGmaker game), but it has some decent scenes)
- Leane 2 - Leane of Legitimate Crown (semi-strong willed FMC, decent plot and scenes, gameplay aint bad either, but long-winded)
- The Great Thunder-Steel Raiouger (strong, agent (plugsuit), red hair. There is some shota in there, but its mostly avoidable.)
- My Girlfriend that was Sold to the Red Light District (strong sweordswoman. but, the entire work is kind of fucked up ngl. and thats some hardcore, non-hidden straight up netorase stuff)
- Iroyoridori (high school setting. girl is on the basketball team. again, she is not really strong-willed in the end, unfortunately)
- 約束と契約のサンクチュアリ~たとえ寝取られたとしても~ ( dont know if i'd recommend it. the corrption build-up is very short and anticlimactic)
Im gonna be honest. I wrote you a bigger list of works I played that kind of covered some of these themes. But the fucking forum logged me out while I was writing it. Im not gonna write it again now. Ill get back to you with some more names. There are a lot more that are just cheap RPGmaker clones but have some of those "strong-willed" FMC and coercion/Type-B NTR tags.
But TLDR is that its super hard to find actual quality games that fulfill all of these criteria anyway. Sometimes it seems almost impossible.
I also got a list of creators who have games in development going in that direction, some of which are coming out soon. Let me know if you'd like a list on that. Although I am not sure if Id be allowed to post actual links on this forum.