Viola kauaensis var. hosakae is a rhizomatous herb characterized by a creeping rhizome and vertical stems emerging from it, with the internodes on the vertical stem longer than those on the rhizome. Its leaves are alternate, with 8-26 mm wide laminae, usually widest in the middle, and shapes ranging from rounded to truncate or shallowly cordate. The leaves are petiolate, and the plant has distinct stipules that are 1.5–5.0 mm long and 1–2.5 mm wide, often overlapping, scaly in appearance on the rhizome, and linear to lanceolate with dentate to erose margins on the vertical stems. The flowers are solitary, borne on terminal peduncles, and accompanied by small, opposite, linear bracts. The sepals measure 2–6 mm long, being elliptic in chasmogamous (open, pollinated) flowers and linear in cleistogamous (self-pollinating, closed) flowers, which enclose all other floral organs and appear withered. In chasmogamous flowers, the petals are elliptic and clawed. The plant typically has five or fewer flowers, up to 3 mm long and 1 mm wide white. The stamens have coherent filaments around the ovary, with the anther connective of the lower stamens extended into an appendage. The fruit is a loculicidal capsule, 7–9 mm long, that dehisces elastically due to rigid keels and thin valve walls. The seeds are numerous, ovoid to globose, with a somewhat leathery, dull testa (seed coat), usually featuring a terminal elaiosome (fleshy structures attached to the seeds), and contain fleshy oily endosperm. It occurs in mossy habitats on nearly vertical slopes or flat ground.