Kamisama mo Shiranai

Due to Yuto's sudden death, Eiji, his elder twin brother, who was merely a college sudent, was forced to substitute for the charismatic vocalist of a popular rock band. The guitarist, Toru, who loved Yuto, painfully watches Eiji, who resembles Yuto, while at the same time, Hikawa, who is Yuto's lover and also the producer of their band, tries to have sex with Eiji as he doesn't know the truth. And then...?

(Source: Countless Time)