Agemochitarō, often affectionately called Mochita, is a small dog who becomes an unexpected but integral member of the Yokoya household. He is a male puppy who was discovered as an abandoned stray left in front of Hitoyoshi Yokoya's front door. His unusual name, Agemochitarō, was given to him by Hitoyoshi and is a creative combination of words. It derives from his round, plump, and fried rice cake-like appearance, blending "agemochi" (fried rice cake) with the common masculine name suffix "tarō". This naming reflects the gentle and whimsical atmosphere of the home he enters.

In terms of personality, Agemochitarō is defined by his friendly and sociable nature. He is an openly affectionate animal who loves people and quickly bonds with the family that took him in. He is especially close to Hitoyoshi and his younger sister, Riko Yokoya, who both shower him with care and affection. His presence is consistently depicted as a source of warmth and lightheartedness, helping to create simple, joyful moments within the household. A key element of his background is a single, precious possession: a fuzzy, plush-covered towel that was left with him at the time he was abandoned. This towel became his most treasured item, representing comfort and security from a vulnerable time in his life.

Agemochitarō's primary role in the story is as a catalyst for emotional growth and a symbol of normalcy. His arrival in episode two is a pivotal event, as it directly challenges the maid, Yuki, who has a deep-seated trauma related to dogs from her past as an assassin. Initially, Yuki is unable to get close to him, blaming herself for being suited only for a life of violence. However, by observing the happy and trusting interactions between Agemochitarō and Hitoyoshi, she begins to see a different way of being. The dog's innocent presence inspires Yuki to wish for a place for herself in this peaceful world and to believe that she, too, can become a normal person. His development is less about his own change and more about the change he incites in others. A notable moment of emotional depth for the character occurs when Yuki accidentally cuts his favorite towel into pieces. Agemochitarō reacts by crying real tears, a display of pure, unfiltered sadness that underscores his deep emotional capacity and attachment.

Regarding his relationships, his bond with Hitoyoshi is foundational as his rescuer and namer, while his relationship with Yuki evolves from one of her fear to mutual acceptance and affection as she learns to care for him. He is also cherished by Riko, completing his role as a beloved family pet. As a dog, Agemochitarō does not possess any superhuman or fantastical abilities. His notable traits are his inherent cuteness, his unwavering friendliness, and his powerful, instinctual emotional honesty. These qualities prove to be remarkably effective in helping the story's human characters confront their own pasts and open their hearts to a new kind of life.