Coccinella, originally named Hiyoko Isshuu, is the youngest Isshuu sibling, representing Sunday in the family's day-of-the-week naming tradition. Five years old and not attending school, she gained the nickname "Coccinella" after her parents died in an accident during an anniversary trip gifted by the children. The name reflects the seven spots on a ladybug's back, symbolizing the seven siblings. This motif deepened when she discovered a ladybug, emblematic of their resilience and new life. Coccinella and her siblings resolved to live independently without adult support.

Characterized as naughty, precocious, and mischievous, Coccinella often argues with her siblings, especially Kaji. She exhibits stubbornness and still wets the bed. Despite this, she is fundamentally friendly and forms the emotional core of the family's perseverance. Her deep affection for animals is central; she owns multiple pets, including two dogs (one named Karabe), a pig, a cat, and a duck, which accompany her daily. This connection fuels her aspiration to become a veterinarian.

While her siblings attend school, Coccinella often visits the zoo to see Kuma, a close friend of her deceased father, or wanders Tokyo's Ueno neighborhood with her animals. She wears her father's heavy wooden geta, which she repurposes as improvised weapons during conflicts, skillfully throwing them or using them like boxing gloves. Her relationship with her siblings involves typical rivalries but is underpinned by mutual reliance and affection as they navigate their challenging circumstances.