40th Period 'Suddenly' / 41st Period 'Duck' / 42nd Period 'Hair Style' / 43rd Period 'Ice'.The dormant classroom heater prompts Yüki, Kazumi, Megumi, Natsumi, and Chika into the health office to warm up and then to begin measuring each other's corporeal dimensions after chasing the school nurse out. Ryöta is twice violently repelled by the girls from resting in the nurse's office due his deteriorating respiratory ailment. After school, some of the students of Class 5-2 discover a lone duck swimming in the school pool whom Kazumi names Kobayashi. When their attempts to send Kobayashi along with a flock of ducks flying overhead all fail and they began discussing how to take care of it, Koyabashi gets its own volition to fly. Yüki, Megumi, Haruka, and Chika interpret Kazumi coming to school one day with her hair in pigtails as license to stylize their own hair that initiates a competition between the four of them that lasts for over a week. Ryöta, Kouji, and Tsubasa engaging in their winter ritual of stomping the ice, before comparing for the biggest piece and then playing with it earns them an austere reprimand from Chika and Natsumi.