Things Hifumi is particularly weak to: being at a pretty girl's mercy.

Nothing wrong with getting dressed up, right? This can come with some 'roleplay within RP' shenanigans (certainly the easiest way to get her into a more dominant mood), or just the outfits themselves being an arousal flashpoint.

For this scenario, there's an open secret: If you approach Hifumi and call her Venus, she'll let you do whatever you want to her. (There are some limits on this - no bathroom stuff, she doesn't eat ass and she won't have her shogi matches or practice compromised.)

Could be as simple as 'they're fooling around in her bedroom and she Cannot be caught by her mother,' or semi-public. Either way, the chance of getting caught is a feature, not a bug.

She might consent willingly to this one, or it could start dubcon and she gets into it as it progresses (just let her keep her boobs).

Not like she wouldn't be curious.