Big Brother's Day. As the day of the decisive battle approaches, Shintaro worries about sending his students to the battlefield. Due to an unknown physical condition, Shintaro was exhausted both physically and mentally. Momen and the others, unable to wait to see how things will go, plan "Onii-chan's Day" out of gratitude for the past. Each of them is enthusiastic about showing hospitality to Shintaro, but...