Brother x Sister (looking for brother)

[Sao]

Blood-related siblings:

Marriage doesn't go well, the husband loves his wife but also enjoys spending time with others. It was his nature, he just couldn't help. Eventually the parents divorced. Just before the court, the wife finds out she is pregnant, but she keeps her mouth shut. She knows the courts are not fair when it comes to custody, usually the mother would win but her husband is wealthy and knows what to do. And she would be technically a homeless woman right after she leaves him. The father keeps the son and doesn't know he also has a daughter. The girl grows up, never know her father and brother. One day the wife dies, the girl is sent to her father. But her father is somewhere oversea and she somehow ends up at her brother's house.

Not blood-related siblings:

A young man, perhaps a college boy living with his family, has always had a problem with his younger sister. She is always the golden child and he is the abandoned one. He knows she deserve that, she's sweet and talented, but he also is jealous with her. Because of her, their parents always think of him as a loser. One day he decides to teach her a lesson, just to scare her a little. Maybe he locks her in a freezer room or have someone kidnaps her... he doesn't want to make it too far but things just go out of control. In the end she dies,he is the one at fault, however. He feels guilty, yes he did. Despite how much he hates her, she's still his little sister. Yet, now that his sister is gone, he would enjoy being the only child.

Having lost her lovely daughter, the mother almost goes crazy and has to stay in a hospital for a while. She then meets a young girl there, who has lost her memory and parents during a car accident. The family soon adopts the girl, now the boy has a new sister. Now what would he do to her? Would he make up for his mistake and love her like a real brother, or would again get risk of this unwanted sister?

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