Ichihachi's name numerically signifies "one-eight," embodying the Armalite AR-18 assault rifle—an American-designed weapon with prominent Japanese manufacturing ties that mirror her mixed heritage. She is the biological sister of Ichiroku (M16A4), though their kinship transformed into a foster relationship after Ichiroku's adoption by the Colt family left Ichihachi with the declining Armalite line.

As Funco's (FN FNC) roommate at Seishou Academy, Ichihachi endears the nickname "Hach-chan" from her. Her design incorporates the AR-18’s notorious loose folding stock flaw through perpetually ill-fitting pants, symbolizing the rifle’s reliability issues and causing her persistent discomfort.

Within the core friend group—Funco, Ichiroku, Sig, and Elle—Ichihachi anchors as the "Only Sane Man," exhibiting grounded, observant behavior against their eccentricities. Her perceptiveness surfaces in spotting impostors like G3 disguised as Ichiroku, a detail others overlook. She applies technical nicknames to peers, such as dubbing HK33E "Mimi" for its twin "3s."

She engages in Seishou's combat simulations, wielding her AR-18 during jungle wargames like "Grip and Hold!" and "Sing! Compete!" During a mock battle tournament, she rescues Galil (Israeli Galil AR) from a lake after defeat, sparking an unexpected bond. Galil grows intensely attached, opting to stay at the academy and shadow Ichihachi closely, cementing their peculiar friendship.