Riku Ageha has black hair and blue eyes. His narcissism surfaces through frequent declarations of his own perfection and inquiries to others about perceiving "the god within him," particularly during performances linked to Tsukigami Haruto. Witnessing Haruto in the "Shadow & Lights" musical during his first year of middle school ignited his passion for musical theater and established Haruto as his personal "god." He actively joined every school club Haruto had participated in during middle school.

Attending Ayanagi Gakuen Middle School Division alongside classmate Koki Nanjo, Ageha's relationship soured when Nanjo failed to recognize Haruto's name after Ageha expressed his desire to transfer into the music course to follow Haruto. This led Ageha to develop a profound dislike for Nanjo, deeming him and anyone ignorant of Haruto's significance unforgivable. He shares a close bond with So Hachiya, his teammate in Team Yuzuriha and roommate in dormitory room 208.

During the Halloween OVA events, Ageha participated in an alumni prank orchestrated by Futaba and Saotome targeting First Dorm residents. He collaborated with Nanjo and Hachiya in preparing ghost costumes and executing scare tactics, though his interactions with Nanjo remained contentious during planning. Ageha performed the song "Wanna be Scream?" with Hachiya, Nanjo, Saotome Ritsu, and Futaba Taiga, and also performed "Storytellers" with Hachiya, Ren Kitahara, and Nanjo Koki during the OVA.

Musically, Ageha specializes in songs including "MOON Holic," "Nervous-aid" (a duet with Hachiya), "Knock on Dream!" (a duet with Yuta Hoshitani), and "In A World You Still Don't Know" (a duet with Tsukigami Haruto). His group chat icon depicts the moon. He cites So Hachiya and Nanjo Koki as his weaknesses and expresses no interest in academic studies despite proficiency in music and English.