Tsukasa Tenma. He's the member of the musical group "25 at nightcore". When he was small, his younger sister got hospitalized and since that day she spent almost all her childhood in hospital, and parents mostly were working to afford her treatment. This is why Tsukasa often was alone, but he never complicated, trying to be a good son and brother. But as time went, he was getting more and more depressed. His feelings were to strong, so sekai was created out of them.