Three generations of dogs have gathered at the dog paradise of Futago Pass, living their days in peace after the fierce battle in Echigo. During a scorching summer heatwave, a dog named Ryu arrives seeking help to rescue his friends from a bandit's rampage. Weed, the son of the legendary Gin and current commander of the Ou Army, departs immediately with his comrades to answer the call.

As his son leaves, the elderly Gin begins to show his age, suffering from heat exhaustion. On the advice of his friends, the aging Akita decides to leave the pack temporarily and reunite with his beloved human owner, Daisuke, promising to return once he is feeling better. Meanwhile, another threat emerges in Hokkaido, where Gin's grandson Rigel must contend with a fearsome bear named Ezoma. With the Ou Army split up across different regions, a new ominous threat begins to loom over the unprotected Futago Pass, intending to seize control when the full moon rises. The aging Gin remains with Daisuke, receiving a new collar and reflecting on memories of his earlier years, from his legendary battles with the demon bear Akakabuto to his final farewells with his old master Gohei.