FictionJunction YUUKA (Fikushon Jankushon Yūka?, though it is usually in English) is a Japanese pop duo, part of Japanese composer Yuki Kajiura’s solo project FictionJunction, consisting of Yuuka Nanri (vocals) and Kajiura (composition, lyrics and keyboards).

The pair first met at Minami Aoyama Shōjo Kagekidan (南青山少女歌劇団, South Aoyama Female Opera Group?, also called Nanshō), a stage group for teenage girls where Kajiura wrote music for some of the plays and Nanri was a performer.

Their first recording was "Akatsuki no Kuruma" (暁の車, Wheels of Dawn?), an insert song in the popular mecha anime Mobile Suit Gundam SEED, though their debut single was the opening of Madlax, "Hitomi no Kakera" (瞳の欠片, Fragments of the Pupil?), released on May 8, 2004. On July 27, 2004, the ending theme to Madlax, "inside your heart", was released. In the same year, because of its popularity and the fact that it was Gundam SEED's one-year anniversary, "Akatsuki no Kuruma" was released as a single, which at its peak placed at #10 on the Oricon weekly rankings and sold over 19,481 copies on the first week.

After a hiatus of exactly a year, Honoh no Tobira, an insert song for Gundam SEED DESTINY, was released, becoming the first seiyū single to hit #1 on Oricon daily rankings.

On November 23, 2005, the duo released their debut album, Destination which placed on the Oricon weekly rankings at #9.

On May 10, 2006, FictionJunction YUUKA released their fifth single after approximately eight months. That year, they also recorded a song, "aikoi", for the Tsubasa Chronicle anime series, which was not released as a single but instead included in the anime's fourth original soundtrack. In November of that same year, they released the opening theme for Sunrise's Bakumatsu Kikansetsu Irohanihoheto, "Kōya Ruten" (荒野流転, Wilderness Vicissitudes?).

FictionJunction YUUKA held their first live concert entitled Premium Live 2007 on February 8 and February 15 of 2007. A new album, circus was announced for release later this year, and two new songs, set to be released on the new album, "Rokugatsu wa Kimi no Eien" (6月は君の永遠, "Rokugatsu wa Kimi no Eien"?) and "Piano" (ピアノ, "Piano"?) were sung at the concert (the first on February 8 and the second on February 15). As Kajiura is handling the music for upcoming anime El Cazador de la Bruja, their 7th single, "romanesque", will become the ending theme of the anime above. El Cazador de la Bruja is produced by Bee Train, which FictionJunction YUUKA has also done songs for previously.