|Occupation||Student (Oshima North Hill Elementary and Junior High School)|
|Anime Debut||Episode 1: "First Operation"|
Momo Isshiki (一色もも, Isshiki Momo) is Akane Isshiki's younger sister. The two of them live with their grandfather, Kenjirou Isshiki, and acts as the motherly figure in the Isshiki family in the absence of their mother Mashiro.
Momo is a young girl with pink hair and gold eyes. She styles her hair into two ponytails in either side of her head and wears a blue tracksuit while at home. At home, particularly when she is doing house chores, she is seen wearing a cream-colored apron with an eggplant design, and has a small wallet, which contains the family's savings, hanging on her neck.
Despite being the youngest of the Isshiki siblings, Momo displays a more mature personality. She is rather intolerant of Akane's habit of hugging their grandfather every time he goes out of his laboratory, and often scolds Akane and Kenjirou whenever necessary. She takes up the role of the mother in the family, taking care of preparing breakfast, buying groceries for the family and managing the family's budget. However, she remains a caring sister to Akane, giving her support whenever she is down.
Reunion at Blue IslandEdit
Momo starts a usual day in their home in Oshima by preparing breakfast, although she is also in a hurry to catch up for a quick shop at a nearby grocery to buy a bargain. After the Isshiki family gathers at the family table, during the conversation in the middle of breakfast, she learns that Akane's friend Aoi will head to Blue Island to undergo medication, and is trying to get her to join her in meeting with her after school. Unfortunately, Momo is unavailable, so to compensate for it, she gave Akane some money so that she can visit their mother at the hospital.
Soon, she and Akane head to school, and she finds out later that Akane tried to test her fear of heights in helping a fellow student get a fallen chick get back to its nest and failed. Momo goes to cheer up her sister and manages to make her smile again.
After school, Momo and Akane quickly head back home to prepare for the reunion for Aoi, but their anticipation became worry as they see a plume of smoke rising from their home. To their horror, they discover their grandfather inside the ruins of his laboratory, and Momo can't help but shed tears upon learning that their grandfather is dead. To their surprise, however, they were able to hear their grandfather's voice, and is coming from the plush otter doll Momo gave her grandfather some time ago.
Kenjirou, now in the form of a talking plush doll, assesses what happened to him, which ultimately involved his latest project going through an unpredictable scenario. During this time, alarms resound through Oshima and an evacuation order was launched. Kenjirou decides to store his body in a refrigerator for the meantime and asks Momo to hide inside the house's specialized emergency shelter as Akane and Kenjirou head towards Blue Island to intercept Aoi, who was in the middle of a battle between a mysterious enemy called the Alone and the defense force of Blue Island.