Katainaka no Ossan, Kensei ni Naru ~tada no inaka no kenjutsu shihan datta no ni, taisei shita deshi-tachi ga ore wo hottekurenai ken~Katainaka no Ossan, Kensei ni Naru ~tada no inaka no kenjutsu shihan datta no ni, taisei shita deshi-tachi ga ore wo hottekurenai ken~ ตอนที่4