Leii possesses blue spiky hair, black eyes, and fair skin. His attire includes a brown jacket over a dark short-sleeved t-shirt, purple pants, long boots, and black gloves, complemented by a golden necklace with a triangle pattern. He wields a sword as his primary weapon.

Personality-wise, Leii generally remains calm, makes rational decisions, and keeps an open mind, though he occasionally loses his nerve. He often presents a gruff exterior to mask underlying self-consciousness.

Raised in Dentro's orphanage in Centvelt, he formed a close childhood bond with Ten and others, a group later known as the Dragons of Centvelt. Leii is an Advanced Replicant created by the Magus Diluculum, sharing a synthetic origin with Ten, Arche, Chica, Emero, and Anzar, making them technical siblings. Diluculum designed them with the potential to join or overthrow the Oración Seis, part of his plan to harvest souls for ultimate power.

During Glaza's invasion of Centvelt, Leii fights alongside Ten. Initially outmatched by the masked commander Zanas, they land a strategic hit on Zanas's armor before Nares rescues them, showcasing Leii's combat coordination under pressure.

In the anime adaptation, Leii's body marking appears grey instead of its game color, matching early concept art. He displays an adaptational jerkass trait, notably teasing Ten with the nickname "Zero Ten." A physical comedy scene shows him sustaining a groin injury when Ten crashes into him after a wagon accident.

Following Diluculum's defeat, Leii and his friends, the Dragons of Centvelt, assume leadership of Felicidad, succeeding the Oración Seis. They guide the continents toward greater prosperity, evolving from orphans to guardians of their world.