The Masked Kid turned Eevee. Once a lowly minion under the command of their master, Lord Stitches. After fighting against him and being thrown out of their dimensional reach, Mouse along with their hilt, Elizabeth IV, fought off the true mastermind. Unfortunately, they couldn't go back. They ventured out into the expanding void, and entered the world inhabited by monsters known as Pokémon. Mouse transformed upon entry. Still getting used to walking in their new state, as Mouse and Ellie learn about this world's rules and look for ways to return home.

Mouse has selective mutism and mostly communicates in sign language (With Ellie's translations if one doesn't understand signing), but will use their voice IF they're comfortable around you. If they're not using Elizabeth in battle, their attacks are Hyper Voice, Shadow Ball, Growl, and Trailblaze.