Shouma Ameku, a 17-year-old male student, attends the same high school as Kiriko Kiyuna and Kōichi Madanbashi. As Kiriko's classmate and boyfriend, he initially confessed his feelings without knowledge of her past as a mecha pilot or her HI-ERO particle abilities, having fallen for her at first sight. Upon learning her secret, he remained steadfastly loyal, prioritizing her well-being despite the complications of her condition.

Pure-hearted and devoted, Shouma actively tries to shield Kiriko from threats like the Penguin Empire, though his lack of combat skills often results in him needing rescue. Their relationship involves frequent public displays of affection, including erotic activities essential for exciting Kiriko to release HI-ERO particles for mecha operations, generating repeated complaints from school staff.

Shouma possesses the unique ability to nullify Kiriko's HI-ERO particles, discovered shortly after witnessing her emit light during excitement. This makes him crucial for managing her energy output. He occasionally serves as her co-pilot, directly assisting in HI-ERO generation by physically stimulating her during battles.

Captured by the Penguin Empire in Episode 10, Shouma is transformed into a penguin, leading him to abandon Kiriko and join their forces. This event galvanizes Kiriko's resolve to save him. Restored to human form in Episode 12 when Six infuses him with HI-ERO particles, he returns to Kiriko's side and actively participates in the final battle against the Empire.

Their relationship exemplifies a Muggle-Mage romance, contrasting his ordinary humanity with her supernatural powers. Their persistent public affection continually draws ire from authority figures like Kazuo Matayoshi and teacher Chieko Kakazu for being disruptive.

His surname "Ameku" combines the characters for "heaven/sky" (天) and "long time" (久), while his given name "Shouma" derives from "general" (将) and "horse" (馬).