Remya mauiensis is a sprawling, many-branched shrub reaching 1-2 meters in height, forming loosely tangled clumps that sprawl on or among other vegetation. The ascending branches are densely leafy along new growth, with young parts covered in dense whitish tomentose hairs. The leaves are chartaceous, narrowly elliptic, measuring 9-18 cm in length and 0.8-2.6 cm in width, with the upper surface initially arachnoid tomentose becoming smoother over time and the lower surface retaining a dense grayish-white tomentose covering. The leaves feature coarsely serrate margins, a long-attenuate base, and petioles that are either absent or up to 1 cm long. The floral heads occur in compact, arachnoid tomentose 5-13 cm long panicles, with peduncles ranging from 0 to 5 mm. The involucre is ovoid to obovoid, measuring 4-5 mm in height and 2-2.5 mm in diameter, with purple-tinged bracts with serrulate margins and an attenuate-aristate to mucronate apex. Each head contains 12-14 female ray florets, with cream-colored rays measuring 0.6-0.8 mm in length and the corolla tube extending 1.5-1.6 mm. The disk florets, between 7 and 12 per head, are male, with campanulate corollas approximately 2.5 mm long and a glandular puberulent surface. The fruit is roughly 1.5 mm long achene, transitioning from glabrate to sparsely puberulent near the base. It grows chiefly on steep, north or northeast-facing slopes in mixed mesophytic forests or montane wet forests between 850-1,250 meters.