Shirakawa begins as a bullying upperclassman at Kin'gyoku Academy, targeting weaker students and rivals from Ōgyoku School, establishing him as an early antagonist. His role shifts when he becomes a subordinate enforcer in Shizune Mejiro's covert group, carrying out her orders for intimidation and espionage. A deep resentment fuels Shirakawa after Kabamaru publicly humiliates him during an intervention. He also harbors an unrequited romantic interest in Mai Ookubo, which complicates his motivations.

Manipulated by Hayate Kirino, Kabamaru's rival, Shirakawa participates in a plot involving drugged candies meant for Shizune but expected to be eaten by Kabamaru. The plan fails when Kabamaru shares the candy with Ran Ookubo, causing her collapse and damaging Shirakawa's standing with Shizune. During escalating conflicts, Shirakawa demonstrates loyalty to Shizune, notably sustaining an injury while protecting her from an attack by Ōgyoku's leader, Shuu Maejima. He later joins Kin'gyoku's collective rescue effort when Hayate, under Maejima's direction, kidnaps Mai Ookubo, aligning himself with the school against their rivals.