Complex sentence: Seinen manga are distinguished from shōnen manga which are for younger boys, as well as the which focus on sex, although some seinen manga like "Xxxholic" share some similarities with "shōnen" manga.
Split into simpler sentences: Seinen manga are distinguished from shōnen manga which are for younger boys, as well as the which focus on sex. Although some seinen manga like "Xxxholic" share some similarities with "shōnen" manga.