Futoshi Kuki is a fifth-grade elementary school student who serves as a supporting character. He maintains friendships with classmates Daiki Nemoto and You Saegusa, forming part of their core social circle. His relationship with Rea Katō traces back to their shared childhood, established long before their current school years.

Futoshi exhibits a notably perverted personality, frequently commenting on women's breasts and acting on emerging hormonal impulses. This trait manifests prominently through his consistent teasing of Rea, focusing on her body shape and weight. His behavior causes her visible distress and fuels her desire for physical change. Despite this antagonism, he intermittently shields Rea from teasing by other boys, revealing genuine underlying concern—though his interventions often prove counterproductive or ineffective.

Physically, he has ochre-colored hair and eyes, complemented by rosy cheeks. Additional details include a birthday on August 8 and blood type O. The dynamic between Futoshi and Rea remains complex, as his persistent teasing coexists with unacknowledged romantic feelings toward her, a contradiction defining their interactions throughout the narrative.