Daiya Koumoto is a main character who exhibits a protective, older-brother-like demeanor toward others, likely stemming from the loss of his parents in childhood, which led him to grow up in an orphanage. During this time, he formed a significant friendship with Rage, becoming very protective of him and introducing him to music, playing a pivotal role in shaping Rage's musical path.

His talents include street dance, with experience competing internationally. Beyond performance, he contributes creatively by designing costumes, accessories, and merchandise for his group. He is a member of the unit REBEL CROSS. Additionally, he co-founded the band CROSS BONE alongside Rage, solidifying their collaborative partnership beyond the orphanage years.

The etymology of his name reflects aspects of his character; "Daiya" combines the characters for "big, great" and "question mark," while his surname "Koumoto" incorporates meanings related to "armor, high (voice), A grade, first class" and "base, root, origin, source." He is visually distinguished by piercings.