Mina Okura is Ryosuke Kaga's childhood friend and neighbor. She developed a notably large bust early in childhood, with measurements noted as 92 cm and an F-cup or G-cup size. Her appearance features shoulder-length brown hair, purple eyes, and she typically wears glasses, contributing to a modest and reserved demeanor that contrasts with her figure. Mina's personality is shy, soft-spoken, demure, socially awkward, patient, and naive. She demonstrates care through domestic support, regularly preparing meals for Ryosuke and visiting his home.

Mina maintains strong romantic feelings for Ryosuke, rooted in his consistent protection during their youth, which established deep trust and affection. She remains unbothered by Ryosuke's overtly lecherous behavior, showing acceptance of his nature. Even after discovering Lisara Restall's identity as a Grim Reaper and the nature of her contract with Ryosuke, Mina exhibits no distress and permits it to continue undisturbed.

To assist Ryosuke in supernatural conflicts, Mina enters a contract with Quele Sellier, Lisara's cousin and fellow Grim Reaper. Under this partnership, Quele derives energy from Mina by listening to her talk about Ryosuke, directly linking Mina's emotional connection to him as a power source. This contract serves Mina's primary motivation: supporting and protecting Ryosuke through indirect means.

Her character arc emphasizes emotional resilience and selflessness, prioritizing Ryosuke's safety and well-being amidst escalating supernatural events. She navigates her partnership with Quele while maintaining her unassuming presence in Ryosuke's life.