Eian leads the Bat Clan of Hida in feudal Japan. His clan adheres to a prophecy foretelling that during the nation's descent into chaos, a foreign ninja wearing a bat mask will arrive to restore order. This prophecy guides Eian's every move and conviction.

When Batman is transported to this era, Eian and the Bat Clan intervene during a critical confrontation, rescuing him from the Joker's minions. Having previously aided Nightwing, Red Hood, Red Robin, and Robin upon their arrival, the clan establishes itself as an ally to these displaced heroes. Eian sees Batman's appearance as the prophecy's fulfillment and pledges the Bat Clan's unwavering support in the fight against the Joker and other villains who have seized territories.

Eian actively fights alongside Batman and his allies. He spearheads the Bat Clan's coordination during pivotal battles, including the river conflict against the Joker's forces and the climactic clash at the "Field of Hell," where villains deploy giant castle robots. His leadership aids in the eventual defeat of the antagonists.

Following the villains' downfall and the return of Batman and the other heroes to their own time, Eian and the Bat Clan assume the responsibility of restoring order and stability to feudal Japan. They are dedicated to healing the land and its society from the widespread chaos inflicted by the conflict.