Crafted by Hiyori's father to ease her grief after her grandmother's death, the humanoid robot Wasimo replicates the grandmother's appearance, incorporating dentures. Its physical capabilities are unconventional: Wasimo moves faster than a snail yet slower than a rhinoceros beetle, but paradoxically outruns bullet trains.

The robot maintains relationships centered on Hiyori, alongside her family members Masao, Papa, and Mama. Secondary connections include Dentures, Hajime, Tsune, Rinko, and community figures such as Catfish Beard Sensei, Murohashi Sensei, and a Lonely Terakawa.