Kokoro is an enormous robotic construct with a female anthropomorphic form, created by the organization Talcus Three. She matches the size of standard PF model mechas from her associated video game series. Her physical design features blue hair, large eyes, robotic antennae or ear structures, and a chain-like restraint encircling her neck. A prominent heart-shaped emblem adorns her chest, reflecting her name's meaning: "heart."

Typically restrained, she receives auditory commands compelling her to fulfill her primary objective: eliminating the target designated Glenn-Leader. Despite these directives, Kokoro experiences human-like daydreams. Within these imagined scenarios, she envisions Glenn-Leader not as her target but as her liberator, directly defying her programming.

Kokoro explicitly voices reluctance to terminate Glenn-Leader due to experiencing romantic feelings towards him. Her aspirations extend beyond combat; she desires marriage to him. She believes this union would trigger a physical maturation process, transforming her youthful form into a fully developed adult appearance and enhancing her capabilities through synergistic integration. This romantic drive forms a core aspect of her depicted consciousness.

Her design and narrative elements show potential influences on later creations. Kokoro's appearance shares notable similarities with the character Nymph from *Sora no Otoshimono*—including blue hair, large eyes, neck restraints, and robotic ear structures—though Kokoro predates this character. Earlier influences on her concept may include the 2003 manga *Q·Ko-chan: The Earth Invader Girl*, featuring similar giant entity themes. These connections suggest cross-media design influences while maintaining Kokoro's distinct characteristics within her original narrative.