Mijumaru was first seen on the Pokémon Sunday set, hiding in the background of the set and Yamamoto was the only one that had spotted it at first. It would disappear whenever Yamamoto tried to get other members of the cast to look at it. It was finally officially revealed in the first episode of Pokémon Smash.
Shoko-tan and Mijumaru were assigned to the Marketing Division (マーケティング部) of Pokémon Enterprise (ポケモンエンタープライズ) where they will promote new merchandise and report the latest Pokémon news.