Yōsei Teikoku (妖精帝國) is a five-member Japanese musical unit formed in 1997. Their music mixes elements of gothic rock, heavy metal, electronic and classical music.

The group name stands for Fairy Empire, in geman — language used frequently on their lyrics — Das Feenreich. The band concept consists of Reviving, through music, the Fairy Empire, which existed between the human world and the spirit realm (known as Spiritua).

They call their fans 臣民 (subject) and their live performances are reffered as 式典 (ceremonies). Each member has a rank (like the military), and the rank changes according to each member degree of contibuition to the fairy empire. Yui Itsuki (伊月ゆい), the vocalist is Yōsei Teikoku 終身独裁官 (Dictator for life). Takaha Tachibana (橘 尭葉), lead songwriter & composer, it’s the captain. Nanami (名波), bassist and composer, is the Warrant Officer. Gight (ガイト), drummer and arranger, is the Sergeant. XiVa (さいば), is the guitarist and corporal. Ryöga (りょーが), is the second guitar and corporal, he Joined the band after Takaha Tachibana’s retirement from live performances.

When a member leave the band they are discharged from the fairy empire military at a ceremony held by their dictator.

Their works include the opening tracks of several anime series, including Future Diary, Magical Pokan and Innocent Venus. They are also really known for their game OST like My-Hime, Queen’s Gate and Super Heroine Senki. After releasing several independent albums, the band released seven major-label albums with their current label Lantis.