Megaton-kyuu Musashi EP5 - Secret Vow

In town, Yamato and his friends see a street gang that Ryugo has a history with. When they follow the gang into their secret hideout, they're surprised by who turns out to be the gang's boss. A fierce scuffle breaks out, but Reiji's appearance interrupts it. Yamato and his friends receive orders to report to base, so they head into battle alongside Reiji and fight together for the first time.