Remya kauaiensis is a weakly erect to scandent shrub, ranging from 1 to 4 meters in height. It forms loosely tangled clumps that sprawl on or among the branches of other vegetation. The stems are leafy near the ends, with younger parts being densely covered in whitish tomentose hairs. The leaves are lanceolate to elliptic-lanceolate or broadly ovate, measuring 4.5 to 17 cm in length and 2.2 to 7 cm in width. The upper surface of the leaves is sparsely arachnoid tomentose when young but becomes glabrate with age, while the lower surface remains densely whitish tomentose. The leaf margins are sharply serrate-dentate to dentate and attach to the stem via 1.2 to 2.2 cm long petioles. The flowers occur in open panicles 10 to 20 cm long and densely whitish tomentose, with stout peduncles measuring 2 to 5 mm long. The involucre is subglobose, around 3 mm high and 2.5 to 3 mm in diameter, with serrulate purple-tinged bracts, especially in the upper half, and has an attenuate-aristate apex. Each head contains 16 to 20 female ray florets, with cream-colored rays varying in length, generally 0.8 to 1 mm but sometimes as short as 0.2 to 0.3 mm. The disk florets are of two types: several outer smaller female florets with narrowly funnelform corollas and several inner larger florets that are functionally female with campanulate corollas. The corollas’ tubes are glandular puberulent. The pappus consists of 4 to 8 bristles, with 2 to 3 extended and the others very short. The fruit is a dry, simple achene, approximately 1.5 mm long and puberulent. It grows on steep, north- or northeast-facing slopes between 800-1250 meters.