I'm surprised to find myself being That Person, but there are at least 1.5 idiots in that room--are we sure there's no backing down from this somehow?
I get the feeling there isn't, but looking at the two principals involved . . .
The most likely possibility would be one or both of them getting too excited to participate in the groping.
I mean basically they might feel like any activity of the sort will basically spiral into full-blown sex, so in fear of taking that step Chiaki will retreat (possibly literally) and then find the life draining out of her because she is physically incapable of surviving without Hana boobs.
Oh lordy, this is why I try to stay out of the prediction business—I just had a vision of Chiaka getting a sudden attack of Mei Aihara Syndrome and insisting on a complete relationship reset so as to do things in “proper” romantic order.
I can’t see Hana putting up with that shit for long, though.