[2] A prequel anime series, Ga-Rei: Zero, aired from October 5, 2008 to December 21, 2008, which details the backstory of key characters Kagura and Yomi.

Kensuke's spiritual awareness and his attraction to Kagura compels him to follow her to the agency, where he is recruited to fight the supernatural.

[4][5][6] Their first enemy is Yomi Isayama, Kagura's former best friend, now an evil spirit due to a stone known as a sesshouseki embedded in her forehead.

[7] The Agency manage to stop her after a long battle, resealing the demon and putting Yomi to rest in the process.

The pressure is building as Kagura starts losing control of Byakuei and the Juugondō arrive in full force.

[24][25][26] Investigations lead the group closer to Naraku, the area in Tokyo destroyed by the Kyūbi and now filled with spirits.

[18] While everyone recuperates from resulting disbelief, government agents arrive to efface them: Izuna sacrifices himself for Yomi, relieving his guilt at allowing her previous deaths.

[18] After resurrecting Izuna with an escort's soul, Yomi arrives at Tokyo's Naraku, releasing all her miasma and disrupting the Reimyaku.

Following clashes with the Tengu, Okama and a revived Kyūbi, they encounter Yomi and Izuna, now a corrupted soul like herself.

In Europe, the series was licensed by Pika Édition for France,[32] by Planet Manga for Italy and by Tokyopop for Germany.

The adaptation was announced on the promotional sleeve wrapper of Ga-rei's sixth volume regarding the green lighting of the show.

It was only later revealed in the second episode and still later in a radio interview with cast members Minoru Shiraishi, Kaoru Mizuhara & Minori Chihara, that the anime in fact tells the backstories of Yomi and Kagura before the events of the manga, thus making Ga-Rei: Zero a prequel to the original Ga-Rei series.

[39] Funimation Entertainment announced Ga-Rei: Zero's English license in August 2010 and released the series on Blu-ray and DVD in 2011.