A feature-length animation of the popular work "Niko Niko, Pun", which began broadcasting in the 1980s as a corner of NHK's educational program "Okaasan to Issho". The original "Niko Niko, Pun" was a live-action puppet show in costume, but in this anime version, the three main characters are voiced by the same voice actors, including Kaneta Kimotsuki. One day, Porori hears from her mother that she has a new baby brother. With the help of Jajamaru and Pikkoro, they set off on a boat to find their brother, but for some reason, the three of them end up on an island inhabited by pirates.

ある日、ぽろりはおかあさんから弟が生まれたという知らせを聞く。じゃじゃまるやぴっころも協力し、船で弟のいるところをめざすが、なぜか3人は海賊のすむ島に着いてしまい…。