I was thinking of saving that for a part two, but maybe it would be a good idea to add that for a 100% final grade...
I reviewed the courses today (just for Japanese lol) again and I was thinking, it would be fun to make the mechanism for unlocking nsfw scenes kind of accumulation-based for future, instead of just a one-time thing for scoring 100%.
The first chapter is fine the way it is. You are learning the basics and stripping the sensei, so those parts are all good. I'd personally only want to see the final part changed cuz I think players should be able to determine what type of relationship you want to have with the sensei (top vs bottom, or perhaps dom vs sub even) w/o necessarily having to score 100% lol, then what future content you can unlock will be based on what choice you make here.
If you scored the passing 90%, you unlock the typical nsfw scene right after making the choice. But if you score 100%, there will be a reward (like a hidden CG or stuff like that) in addition to the typical scene.
For future builds, the number of times you score 100% on quizzes determines how many additional scenes / CGs / elements you can unlock. For example let's say CG2.3 is the first additional CG, it could only be unlocked after you score 100% on two quizzes. Then CG2.4 after scoring three 100%s, special gear (bondage with ropes, leather, etc ;) ) after 5 100%s. So on and so forth.
I didn't go as complex as you suggested, but it's all in the new build J-Raythalos