The protagonist's younger sister, one year his junior. She addresses the protagonist casually without honorifics, and they have a good relationship. Since their parents are away on business and haven't returned, she practically lives alone with the protagonist. She has a bright personality. One day, she is kidnapped along with the protagonist by a dark organization. While the protagonist is unconscious, she is remodeled into a monster. The organization is destroyed immediately afterward, and she escapes with the protagonist, but she now occasionally undergoes a transformation into a monstrous form.

The form Hana takes after being remodeled by the dark organization into a giant monster. Although modified to be a biological weapon, her mobility was poor. Just as they were about to scrap the project, the facility exploded, allowing her to escape with the protagonist. She is nearly 2 meters tall, significantly larger than the protagonist. Her entire body is made of a rock-like material. While she has arms and legs, she has no face, making her expressions unreadable. She loses the ability to produce human speech and can only make low, rumbling growls like "Zzzzz..." Her intelligence is lowered in this state, but as time passes, she begins to act affectionately toward the protagonist.

A shadowy organization plotting to rule the world. They kidnap the protagonist and Hana, remodeling Hana into a monster. However, immediately after the modification, the building suffers a massive explosion because someone forgot to turn off the gas. Everyone except the protagonist and Hana is wiped out in the blast.