Finnian, affectionately known as Finny, serves as the Phantomhive household’s gardener, a strawberry-blond teenager with turquoise eyes and a boyish face framed by red bobby pins. His casual outfit—a red-piped shirt, plaid trousers, and knee-high boots—is topped by a straw hat gifted by Ciel Phantomhive, deliberately worn to hide the "S-012" brand etched into his neck, a scar from his past as a fugitive test subject. Enhanced with uncontrollable superhuman strength from institutional experiments, he inadvertently damages surroundings he cherishes, including the manor’s gardens, balancing his physical might with a guileless, tender-hearted nature prone to tearful outbursts over mistakes.

Rescued by Ciel and Sebastian after escaping captivity—where he endured forced participation in fatal experiments and a doctor’s killing—Finnian pledges fierce loyalty to the household. Beyond tending plants, he aids in defending the estate alongside servants Mey-Rin and Baldroy, confronting threats like the Noah’s Ark Circus intruders during the Circus Arc, where he battles invaders despite his aversion to violence. His trauma from confinement fuels a preference for open-air labor, avoiding enclosed spaces whenever possible.

Though often cast as a clumsy comic figure, Finnian reveals quieter resolve when tending to Ciel’s well-being or safeguarding the manor. His growth unfolds through incremental triumphs, such as mastering his destructive impulses to nurture gardens he once ruined. Collaborative dynamics with fellow servants highlight shared dedication to maintaining Phantomhive operations under Sebastian’s exacting oversight, blending camaraderie with duty. His arc traces a path from fractured hesitation to purposeful enthusiasm, anchored by loyalty and an evolving grasp of his own strength.