Mina Kuroki is the elder sister of Gai Kuroki, left on Earth when Gai was transported to the Heavenly World (Tenkūkai). Her story unfolds solely in the OVA "Tenkū Senki Shurato: Sōsei e no Antō". Overwhelmed by grief and loneliness after Gai's disappearance, Mina's subconscious summons Scrimil, an entity claiming to be a "deity of harmony" wielding significant power across Earth and Tenkūkai.

Driven by Mina's unresolved sorrow, Scrimil aims to forge a new universe where she and Gai coexist without separation, manipulating reality and threatening both worlds. Scrimil manifests through a pierrot doll and a clown puppet during his actions. His plan triggers the disappearance and ambush of several Eight Guardians (Hachibushu), forcing the guardians to investigate Earth.

The climax reveals Mina as Scrimil's true origin, the entity born unknowingly from her intense longing and pain. Her desperate desire to reunite with Gai fuels the OVA's central conflict. Confronted by the guardians who uncover Scrimil's link to Mina, the resolution focuses on addressing her core grief. The separation from her brother is acknowledged as the catalyst for the reality-altering events. Mina's arc concludes with this revelation, ending the immediate threat while the emotional weight of their permanent separation remains.