The series follows Weed's offspring: Bellatrix, Rigel, Sirius, and in particular, Orion.

An earthquake and subsequent volcanic eruption separates Orion from his parents and siblings. With the Ōu Mountains in complete disarray, new threats arrive to exploit its weaknesses. Three sons of the Irish Wolfhound Kamakiri, a platoon leader for Hōgen, wish to avenge their father's death.

Meanwhile, Kurohabaki Masamune, the leader of the Kurohabaki Clan of ninja dogs, aims to take over Ōu, gathering recruits and killing those who resist.