Asaka Narumi debuted as a minor Foo Fighter antagonist in the first arc, approaching cardfights with theatrical flair and treating battles as entertainment, often toying with opponents. Her defining trait is fierce, singular devotion to Ren Suzugamori, compelling actions like deliberately failing college admissions to stay in his academic year.

She reappeared in the second arc transformed into a PSYqualia Zombie under external control. Even infected, her attachment to Ren Suzugamori created intense internal conflict; she experienced a PSYqualia premonition of defeating him, interpreting it as a horrifying nightmare. This dread directly caused hesitation during their confrontation, preventing her from fully engaging against him. Ren Suzugamori deliberately fought her to shatter this psychic control and restore her.

Freed from the PSYqualia Zombie state, she later assisted at Card Capital alongside other recovered individuals while the main protagonists confronted remaining threats. Her loyalty to Ren Suzugamori remained evident when she joined him on the Fukuhara High School team for the Vanguard Koshien tournament, adopting their standard female uniform. During qualifications, Kouji Ibuki specifically sought a cardfight against her to secure his own spot on Fukuhara's team as part of his character development.

Her surname "Narumi" combines the Japanese words for "ringing" (鳴) and "sea, ocean" (海).