For this game, or series if a Nun partner continues but guessing they may keep them petite like Hajaan to reflect they lack of combat ability, I think they could have Hajaan scenes being based on her interacting with the town NPC.
The more game overs and defeats Lilia gets the more scenes Hajaan will have involving her being raped or having sex with the more aggressive town male NPCs and scenes showing her being raped by tentacles, demihumans, slugs, monsters, and cultists that sneak into the town with her own pregnancy scenes as well.
They can have these scene trigger by the Main Character return to the Church and find where she normally is empty and just interact with that spot with Lilia wondering where Hajaan has gone to then the scene changes to show Hajaan's H scenes. After that Hajaan returns to her spot but you see obvious effects on her such as her being pregnant or some other negative effect that has made her more addicted to sex and corrupted. Leading to scenes where Hajaan will eventually give birth and return to the church later without Lilia suspecting anything due to Hajaan brushing her back to normal state as she purify herself. This can be also a trigger for a side story involving Hajaan to show how the town becomes more corrupted while Lilia is away.
If they cannot do this in this game for future updates then maybe in the third game SiNiSistar 3 so they have some kind of H scene consequence for getting constant defeats and game overs while providing more scenes for the Main Character's partner.
) ending where you become a town bicycle and they just gang bang you out in the town square in front of everyone. Maybe also have Haanja observe in horror / disappointment in the background about what you became. Or just have the bums take her too once they get the idea that the sisters are not allowed harm them in order to resist them (as the lore bit in the gallery says).
