NSFW Warning: this question is related to hentai anime.
A piece of music is used in different anime, namely ED of Sleepless: A Midsummer Night's Dream - The Animation, and the BGM starting from 11:50 in Ep. 2 of Jashin Shoukan: Inran Kyonyuu Oyako Ikenie Gishiki. The two anime have different producers and studios, the games have different developers. How can the music be used in both?