Yosuga no Sora

On their way home from school, Haruka and Kazuha are interrupted by a frantic Yahiro, who is concerned over the non-appearance of the always-responsible Akira as usual. They discover Akira at her home, collapsed due to exhaustion, and Kazuha proceeds to blame herself and her infatuation with Haruka for not noticing Akira's condition.

When Kazuha realizes that Haruka has overheard their conversation, she chases him down to clear up any misunderstanding. She reveals that Akira is, in fact, her illegitimate older sister, born of a different mother. Due to her family's societal standing, Kazuha's father is not able to acknowledge Akira as his daughter, causing Kazuha to be resentful of her father and to feel a burden of guilt and responsibility towards the always-hard-working Akira. To help lift Kazuha's spirits, Haruka invites her out on a date, and they subsequently realize and admit their rapidly-progressing feelings towards each other. Meanwhile, Akira continues to try her best on her own, but collapses, apparently due to exhaustion.