From my testing, NPCs become more inclined to fetishes when they participate in them and had an overall enjoyable scene. Same is true for the opposite, fetish inclination will drop if they had a bad experience.
Decreasing sensitivity is simple: let the "overstimulation" text hit red and continue stimulating. Otherwise, sensitivity will increase as long as there's no overstimulation text or it remains below 100%
Liliths throne? It's text based with more progress on everything being doing able over more detailed but locked content so interations and game play can become a bit rinse n' repeat but also means that 90% of the game can be done with all and not just with 1 person or in 1 person story