Airu Inuzuka is Romio's older brother and assumed leadership of the Inuzuka family after their father's passing. As the second-year Head Prefect for Dahlia Academy's Black Dogs dormitory, he projects a strict and serious image, especially toward Romio, motivated by protecting the family name from perceived dishonor. His disapproval of Romio's hidden romance with Juliet Persia intensifies his surveillance, culminating in a direct holiday confrontation where he uncovers Juliet's disguise. This leads to a decisive duel challenge. Romio's victory compels Airu to recognize his brother's commitment to uniting their rival nations, forcing a reluctant acceptance of the relationship and a pledge of future support, though he remains cautious.

Airu's personality merges stoic authority with deep-seated familial loyalty. He demonstrates kindness to family, shielding Romio from their mother's dramatics and later mentoring Leon in the Student Council. His leadership prioritizes duty and discipline, yet subtle concern for Romio sometimes surfaces beneath his harsh exterior. Following his defeat by Romio, he resigns as Head Prefect, enabling Romio's ascent to the role while adopting a more supportive background position. His interactions with Black Dogs prefect Kochou Wang suggest potential romantic interest, indicated by her affectionate nickname "A-chan" for him.

Over the narrative, Airu transforms from an antagonistic enforcer of tradition into a tacit ally for Romio and Juliet's cause, embodying a shift toward reconciling their nations' long-standing feud. His character arc concludes with his attendance at Romio and Juliet's wedding seven years after graduation, reflecting his enduring, albeit reserved, commitment to their union.