Mii

みい

Mii, the youngest sister, is an 11-year-old girl who is by far the most energetic and naive of the three. Her light-purple hair is usually tied in a double-bun, except when she cosplays as "Magical Girl Mii."
Mii is obsessed with defining plush things—especially girls' breasts—and constantly touches objects, especially people. Due to her young age, she is quite naive and energetic. Although she travels through time like the other girls, her naivety and energy allow her to overcome most of the jumps with ease.
"Magical Girl Mii" was a specialized cosplay costume she created in the episode where she met a chronically ill girl she attempted to cheer up. It apparently cost a lot of money, but Ai seemed easily able to pay for it. Afterward, she often wears it around, pretends to help stop evil, and believes she has superpowers. Later in the episode, the girl collapsed from overexertion while playing with Mii. Mii tried to use the powers she thought she had to heal her friend. The attempt was successful, and Ai revealed to the viewers that Mii's special power was healing. However, Mii remains unaware of this for a good portion of the season and continues to believe that she has other powers as well.