Yōsei Teikoku (妖精帝國, lit. "Fairy Empire"; German: Das Feenreich) is a five-member Japanese musical unit formed in 1997. Their music mixes elements of gothic rock, heavy metal, electronic and classical music. Their works include the opening tracks of the several anime series, including Future Diary, Magical Pokan, Innocent Venus, Kurokami: The Animation, The Qwaser of Stigmata, Big Order, and the Tokyo ESP soundtrack. After releasing several independent albums, the band released seven major-label albums with their current label Lantis: Gothic Lolita Propaganda, metanoia, Gothic Lolita Doctrine, Gothic Lolita Agitator, Pax Vesania, Shadow Corps(e) and The Age Of Villains.
Yōsei Teikoku (commonly spelled as "Yousei Teikoku" in Romaji) is led by vocalist Yui, whose official title is "Dictator for Life" (終身独裁官). She bestows honorary titles on the band members as part of the Fairy Empire.