Donten ni Warau Gaiden: Ketsubetsu, Yamainu no Chikai

One year has passed after the great battle against the Orochi (gigantic snake). Kumou Tenka had been paralyzed from the final battle and he took part of the government’s human experiment before the battle. Tenka withdrew himself from society but his younger brothers Soramaru and Chutaro find out the secret past about their older brother.