One morning, Gintoki, Shinpachi and Kagura wake up in darkness. “Wake up,” a voice in their heads says. The three are unable to understand the situation and go back to sleep. “Release your inner power,” the voice persistently tells them. But Gintoki and the others ignore it and stay fast asleep. Offended by their rude behavior, the owner of the voice shows himself. Amazingly, it is Lake Toya, the immortal who lives within Gintoki's wooden sword! The immortal tells them that he will teach them powerful secret techniques. In response, the three…