Nuumamonjaa takes place in the same setting as Chrono Trigger during the night before the beginning of the game's events. It follows two monsters from the game, a Nu and a Mamo (called Kilwala in the English version of the game), voiced by Chafurin and Mayumi Tanaka respectively, through various adventures. These all take place in the "Millennial Fair", the festival at the beginning of Chrono Trigger, which in the anime has been infested by a festive gathering of monsters coming through portals. They meet several characters from the game, including Johnny and Gonzalez (called Gato in the English version of the game). The anime ends with a scene from the following morning after the monsters have all left, in which Crono and Lucca can be seen. The credits show Nu and Mamo parodying scenes from the game.