Yuri Eberwein

ユーリ・エーベルヴァイン, U-D / Unbreakable Darkness
Yuri is known as the Leader of the Purple Sky which comes from the Tome of the Purple Sky. Mah Shjo Lyrical Nanoha As Portable THE GEARS OF DESTINY: Born in the Ancient Belkan ages Yuri was originally a human. However due to a program written with the aim of overwriting the Book of Darkness Yuri was turned into Unbreakable Dark aka System Unbreakable Dark shortened as UD until the separation by the end of The Gears of Destiny. Mah Shjo Lyrical Nanoha INNOCENT : Yuri Eberwein along Stern Levi and Dearche is a student studying abroad in Uminari City. Source: Nanoha Wiki