Kyoko Kuroyuri leads a double life: as the steel-wielding operative Steel Princess for the Secret Society Gekko, clad in light purple and grey seamon-themed attire bearing Gekko's insignia and a concealing mask, and as a long-haired, bespectacled high school student with a notably developed physique noted among peers. She attends Kokutei High School under Gekko orders alongside other Princess Series members, serving as student council president.

Initially quiet and lacking confidence, Kyoko confided her romantic feelings for Culverin Bear to friends Kiki Majima and Desumi Magahara, doubting her femininity. Desumi's attempt to enhance Kyoko's charm backfired, causing Kyoko to withdraw. Reassured by Desumi that authenticity mattered more than change, Kyoko reconciled with her and found the courage to confess to Culverin Bear, beginning a relationship.

This relationship significantly boosted Kyoko's confidence. She publicly teased Kiki about being single during the Kokutei Festival while accompanied by Culverin Bear in costume. Though briefly separated in the crowd, they reunited, displaying their bond. They later coordinated effectively in combat against adversaries like the Gelato 5.

Kyoko maintained a teasing friendship with Kiki Majima, participating in group activities like Desumi's sleepover. During an incident involving nurse Kira Sanzugawa, Kyoko succumbed to infantile brainwashing alongside Kiki. Later, confronting Gekko's creation, the Ultimate Phantom, Kyoko fought in distress after it consumed Culverin Bear. Captured herself, her steel powers were used to ensnare Kiki. Both were freed following the Phantom's defeat by Red Gelato and Reaper Princess.