Hattori counts down to a particular day that comes once every four years. We know what that is, don't we, folks? Yes. It's the 29th of February - the leap day. Hattori is excited as it's the day before the leap day, and so are the others.
The next day, Hattori and the gang hoist a flag and rejoice for becoming friends in the first place. Hattori, instead of his Ninja Robes, is wearing Western clothes - and so is someone else... uh-oh. It's the sloppiest, touchiest, most infatuated girlfriend in the world: Tsubame. She turns up, wearing a pink dress with a yellow collar, and immediately starts fawning over Hattori.
Back to the subject, Hattori and Tsubame set off in the direction of a theme park. They jump out of the bedroom window, roof-surf to town and stroll along the pavement to the fair - when we meet the most evil, ruthless and slimiest git in the world: Kemuzou Kemumaki and his cat. They try to block the way to the entrance, but Hattori and Tsubame evade them before submitting their tickets. Kemumaki tries to follow them, but the guard slows him down.
Later on, Hattori and Tsubame ride a carousel. Hattori performs Ninja horse stunts his father taught him on his horse, but then gets told off by another guard for performing dangerous stunts. Kemumaki tries to evade them a few more times, but Hattori shakes them off.
Kemumaki and Kagechiyo go home, grumbling as they see Shinzo and Kenichi walk home after a baseball match. They then come up with a good idea: ambush the gang at night.
Later that night, while Shinzo and Shishimaru doze in Kenichi's bed, Hattori, Kenichi and Tsubame play Rock Paper Scissors. Kenichi keeps losing to Hattori and Tsubame, but then Hattori loses to Kenichi and Tsubame. Kemumaki turns up, ready to attack, but he's too late: the clock strikes twelve, the day becomes the 1st of March, and Kemumaki is left dismayed.