Domo Arigato, Aki Roboto!

Kururu proposes a formal competition to compare human and Keronian physical proficiency. Natsumi, still seething after the events of episode 17, accepts Keroro's challenge, whereupon Keroro picks Fuyuki as his opponent. Momoka's snowy mountain complex forms the backdrop as Keroro and Fuyuki go to battle in winter sports, but one unexplained phenomena after another (a freak updraft, a stray missile, a bobsled rail coming off for no reason) threaten to throw the competition into disarray.
All the happenings in the first act are finally explained - Kururu's true intention was to build and test his new giant robot (which eager test pilot Hinata Aki dubs the Autumn H), without unnecessary distracions from the Hinata children and his fellow soldiers. Unfortunately Aki goes crazy with the robot's weapons, forcing Kururu to move out in the Kururu Robo to bring her in, resulting in all the unexplained phenomena from the first act.