Leviathan's older brother is a human male with waist-length blue hair and purple eyes, hailing from Aquafall. He served as Leviathan's childhood water magic instructor, under whom her abilities surpassed her current prowess despite her youth. He vanished after embarking on a journey, leaving his staff—alternately called a lance—with Leviathan. She retains and regularly wields it as both a memento and magical implement.

His unexplained disappearance drives Leviathan's narrative arc. She actively pursues clues about his fate, questioning locals in venues like the Key Tail tavern, yet uncovers no leads. Fearful of missing his potential return, she confines her search to their hometown, refusing to venture beyond its borders.

Exclusively appearing in flashbacks—first in Episode 1—he is depicted mentoring Leviathan in water magic techniques. His absence fundamentally shapes her character, fueling her shy demeanor and wavering self-confidence as she longs for his homecoming while wrestling with the mystery of his departure.