Akuma de Tenshi: Umare Kawatte mo Soba ni Itai

A romantic comedy(?) about a serious, devoted angel and a foolish devil. The devil, tired of his boring daily life in hell, chooses death and wakes up with a baby angel in his arms! The baby angel is Ell, come to bring the devil back to heaven. In fact, the devil was once Ell's twin angel named Allen! In order to return to heaven, it seems that a ceremony must be performed to send the soul to the "Gate of Reincarnation". If successful, Allen's soul will be purified and he will be able to return to heaven, but he has no interest at all. However, one day, the devil Allen suddenly reminds Ell of the angel Allen of his past. Even though he has no memories and is now a devil in body and mind, he is still his beloved Allen - and the moment his heart beats with excitement, Ell's appearance suddenly transforms into an adult!? (Source: Melty Night, translated)