Ralsei is depicted as a short Darkner. He initially wears a hooded, dark blue cloak which obscures his face, resembling the River Person. During Chapter 1, Ralsei's pointed green hat covers his horns, concealing his entire face in shadow. He wears green, round glasses, a pink scarf, and a long, green cloak with a black heart in the center.
At the end of Chapter 1, Ralsei resembles a boss monster. His face is similar to Asriel's Undertale counterpart, with the exception of glasses, pink shaded horns, and pink fur accents. Without his glasses, his eyes are visibly pink-colored with detailed eyelashes and what appears to be pink eyeshadow.
In Chapter 2, certain details of Ralsei's robe change compared to his Chapter 1 appearance. The sleeves on Ralsei's robe change to black, the edges become more uniform rather than appearing tattered, and the emblem on his chest appears to change from a heart to an inverted spade. The latter matches early concept art by Temmie Chang. This element is only present on some of his sprites, with most of his in-battle sprites and some of his overworld sprites reverting to a heart emblem.
