Danjo no Yujou wa Seiritsu suru? (Iya, Shinai!!) - Ch. 8

[ItsThatBriGuy]

That was really surprising. Her face here kinda looked like she had regret and felt guilty towards him.
And in ch 1, he said he was never good with his sister even before he met Himari. So, was there an event in the past (before Himari) that made their sibling relationship this way?

Spoiler

It's heavily implied (through the portion of V4 I'm up to, anyway) that she has a difficult personality in general (Hibari was quite interested in her in high school but never could crack her shell, giving Kureha a chance to get between the two of them).

She also seems to carry some resentment towards Yuu (like their older sisters) for having a path out of the family business, while her super-genius self is stuck there.