Little sister wears the pants in this incestuous relationship.
It's not incest yet. This all could easily be interpreted as Hana wanting to capitalize on a possibly once-in-a-lifetime chance to see one of her elder sisters in such an embarrassing, vulnerable position.
... which would be the perfect setup for Hana later lying in bed while self-satisfiedly musing over the leverage she now has over Kuki, only to be blindsided by someone entering her (pitch-dark) bedroom and - with Hana pretending to be asleep just to see what this mystery person wants - stealing her first kiss. The shock and confusion from both having the unthinkable actually happen to her and realizing that she actually liked the kiss and even wants more from where that came from would keep her frozen long enough for the culprit to make a speedy escape, leaving Hana hot and bothered as well as completely in the dark about who was it that kissed her.
It's not incest yet. This all could easily be interpreted as Hana wanting to capitalize on a possibly once-in-a-lifetime chance to see one of her elder sisters in such an embarrassing, vulnerable position.
... which would be the perfect setup for Hana later lying in bed while self-satisfiedly musing over the leverage she now has over Kuki, only to be blindsided by someone entering her (pitch-dark) bedroom and - with Hana pretending to be asleep just to see what this mystery person wants - stealing her first kiss. The shock and confusion from both having the unthinkable actually happen to her and realizing that she actually liked the kiss and even wants more from where that came from would keep her frozen long enough for the culprit to make a speedy escape, leaving Hana hot and bothered as well as completely in the dark about who was it that kissed her.
I'm pretty sure the whole stolen kiss thing was thrown out/an alternate reality after Mochi au Lait decided to make a more fully-fleshed-out story with these characters.
But yeah, she's tempting a bit of fate for the tables to turn on her, although it depends on how much the artist likes this sort of younger-girl-blackmails-her-elders setup (and given that it's Mochi, there's a decent chance she can carry on with this power dynamic for quite a while...)
Then...Because I want to see it.And that is non-negotiable.Uuuuugh...If you don't like it, then you shouldn't have done something like that in the first place.If I suck it up and wear the swimsuit, will you promise not to take pictures...?That's also not happening.Why!?It's so I can blackmail you again in the future.Blackmail...?It's my reward for uncovering your evil deed, Kuki-neesan.