Soshite Hatsukoi ga Imouto ni Naru

Having faced many hardships as a child, the cynical Kazuharu believed that the world was a wasteland and the only way to survive it was to work your hardest. There’s no time for playing nor falling in love, like the rest of his classmates.
While he was working hard as usual, he saw a mysterious girl with a uniform he did not recognize. She appeared to always avoid the gaze of others. Normally he wouldn’t pay much attention, but for some reason he was particularly interested in her. Then suddenly one day, she became his imouto.

Japanese Version