Lethe has long, light brown hair with uneven bangs and yellow eyes. Part of her hair is braided and held in place by a large off-white ribbon. Her ears are pointed and a pair of off-black horns protrude from her head. She wears a dark gray knee-length dress with red-orange lining, as well as an off-black corset vest with a feathered collar. A pair of crosses are attached to the ends of her vest and another, red-orange, garment is visible beneath. She also wears a pair of light gray flared sleeves beginning at the elbow, which end in off-white frills at the bottom and are feathered at the top, and accented with small red-orange bows. A pair of off-white gloves cover her hands and yellow-orange sleeves cover most of her upper arms. She wears light gray stockings and dark gray platform heels. Lethe wields a large, elaborate scythe with an off-black horned skull attached to the end opposite the blade. She is generally depicted holding it by the skull and not the handle.

Arcaea
Arcaea are melodical shards of the past that call out to the girls, but each chooses to be experienced only by one or the other. Over time, the girls begin to notice inconsistencies in the Arcaea that choose them and develop conflicting views about the world as it once was.