This is a remix/arrange of Flandre Scarlet's themesong: U.N.オーエンは彼女なのか? (U.N. Owen was her?).
You can find Flandre, and her theme in the game Touhou 6: Embodiment of Scarlet Devil.
Track Title: House of Flandre
Original Title: U.N.オーエンは彼女なのか?
Arranger: cYsmix
Group: cYsmix
Album: Secret Princess
Link: http://youtube.com/cYsmix
http://www.twitter.com/cYsmix
Release date: 2012-01-29
Image source: http://safebooru.org/index.php?page=post&s=view&id=714447