Unsealed, The Zero Drive

Riku has regained his memories and is reunited with Kogenta. He also meets Yakumo again, who tells him about the Fukumaden and the past. There once was a man named Utsuho, and he had the terrible power to control the Youkai. He used the Youkai to attack Kyoto, the capital city at the time. The Toujinshi used their power to fight Utsuho and eventually won.

Synopsis excerpt via Kitsu.