Hiyori is an elementary school girl who cried every day after her grandmother passed away. In response to her grief, Hiyori's father built a humanoid robot named Wasimo, designed to resemble the deceased grandmother and fitted with dentures, to provide comfort and replace her presence.

Hiyori interacts with Wasimo as it meets various people and experiences different events. The robot walks at a speed faster than a snail but slower than a rhinoceros beetle, yet it possesses the capability to run faster than a bullet train.