"Kōya Ruten" (荒野流転, Wilderness Vicissitudes) is the sixth single of J-pop duo FictionJunction Yuuka. It was released on November 22, 2006. This single included opening song of the anime Bakumatsu Kikansetsu Irohanihoheto, as well a song from the musical Angel Gate: Haru no Yokan (Angel Gate: 春の予感~) in which Yuuka Nanri, the vocalist of FictionJunction Yuuka, stars in. Both songs were composed by Yuki Kajiura. Its catalog number is VICL-36177. This single peaked at #13 on the Oricon weekly charts.