I do like the idea of the different body types for the female characters if the author so chooses. Also the minigame recommendation you gave as I can see that definitely connecting with the dating potential to this game if it decides to delve deeper into it. I can't really imagine any other ways to add on other what your comment placed in so yea. You said it.
I would like add on a bit to the "Relationship" level you mentioned, you think a special animation or reward for the player should be made if they were to reach a potential max level relationship with a character? Maybe a perk that modifies the gameplay a bit on their barns / huts?
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Other than my personal preferences such as lactation and impregnation which isn't everyone's taste (if it was implemented the bunny girls first). The neck nibbling used in one of the minigames you mentioned or licking definitely sounds enticing.
I'm more into animations and what things an artist would make for these kinds of games, an example being fingering animation while having breast sucking or fondling as she's laying down or against the wall is one. Or a reverse piledriver (hopefully on the bunny girl) but she can rest her lower half against a wall if needed and the MC can penetrate a little easier without worry for the bunny girl's lower half to be pushed back or use props to help hold her in place. Seashell position is a classic one.