Story
OVA by ZEXCS — Fall 2011, 1 episode, Finished.
According to the official website, an OVA of Itsuka Tenma no Kuro Usagi was announced to be bundled with the ninth volume of the novel. An animated crossover between Itsu-Ten and The Legend of the Legendary Heroes (Densetsu no Yuusha no Densetsu or DenYuuDen) fantasy story.
Synopsis via AniList (English).
