Mamamametchi, mother to Mametchi and wife to Papamametchi, lives with her family on Tamagotchi Planet. When Mametchi's invention accidentally brings the human girl Tanpopo to their world, Mamamametchi and Papamametchi appear alongside their unhatched egg, reassuring Tanpopo they will build a rocket to return her home precisely when she left.

Later, Mamamametchi and Papamametchi leave Mametchi and Tanpopo to watch their egg. Before departing, Papamametchi gives Tanpopo a key essential for her return once the rocket is ready. During their care, the egg accidentally rolls out of the house, becoming dangerously stranded high on a building. Mametchi risks his life to retrieve it, leading to a fall that also endangers Tanpopo and Memetchi. KuroMametchi saves everyone by bouncing them off Kuchipatchi. Mamamametchi and Papamametchi express no anger toward Mametchi, recognizing his responsibility and effort in protecting the egg. The egg soon hatches into their daughter, ChaMametchi.

When a sudden illness strikes Tamagotchi Planet after the sun entity Sunnytchi vanishes, Mamamametchi participates in the response. As Mametchi, Tanpopo, and friends secretly launch a space mission to find Sunnytchi, Mamamametchi appears via video call with Papamamatchi and other scientists, demanding their return. After Mametchi explains his responsibility, they relent. The scientists reveal a medicinal capsule mounted on the rocket to cure the planet. After the cure and subsequent space dangers, Mamamametchi joins the collective effort to awaken the cosmic entity Blackholetchi, whose gravitational pull threatens the rocket. Her voice, combined with the entire planet's population, successfully awakens Blackholetchi.

Following the crisis resolution, Mamamametchi attends the celebration for the Gotchi King's birthday and participates in Tanpopo's farewell when she returns to Earth.