Modeus, like most of the Helltaker cast, is depicted as a short demon girl with pale skin, red irises, a black arrow-tipped tail, and silvery-white hair. Her hair is wavy and unruly, with several notable cowlicks of hair dispersed in no particular pattern. She has a left-swept fringe that stops at eyebrow's height, as well as two long segments of hair in front of either ear that drop down to chest-height, ending in a zigzag shape. While her irises are still red, rather than black pupils she has luminescent white pupils in the shape of hearts, and under her eyes is an always visible blush, though intensity varies. Adorning her head are two simple black horns pointing up, as well as many hearts that form a vague circlet around the sides and back of her hair.
Modeus has a figure commonly associated with models or adult actresses, with a large bust, small waist, and wider hips. In her idle state, she appears with her hands resting on her chest, wearing a black blazer with a red turtleneck sweater underneath, a black pencil dress split on both sides, and red leggings.

Modeus at first appears to be the quintessential lust-crazed demon; upon first meeting Modeus, she immediately demands that the Helltaker do her right then and there. She continues to exhibit this hyper-sexual tendency in the next level when the player asks for life advice, to which Modeus replies with, "Advice? Easy. Skip all the puzzles, gather all the ♥♥♥♥♥♥♥ and let's engage in proper harem activities", meaning that she is impatient for the event of the harem. Pandemonica asks the Helltaker to forgive Modeus, and explains that most demons are like Modeus because "Lust for sin is in our blood" and that it is "hard to keep in check". However Modeus, while very sexually charged, is somewhat naive towards concepts like romance, as shown in the post-game level where when interacted with she is seen to be reading a romantic comedy. She says she's never heard of romance before but thinks it is kinky, and when asked about going on a date by the Helltaker, she becomes flustered and calls him a "perverted degenerate."

The player meets Modeus after completion of Level 2, where they are greeted with Modeus commanding "You and Me. Now", inferring sexual intercourse and ignoring any formal introduction. The player is then greeted with two response options:

"Deal. No questions asked."
"No time. Busy gathering girls."

Should the player choose the first option, Modeus will mention that "They always say that... and they always try to run away." She then explains that she'll have to break your legs just in case, and the player receives a "Bad End" screen, where it reads that Modeus took out a sledgehammer and that "It is not going to be pretty."

Should the player choose the second option, Modeus will inquire about whether the Helltaker is trying to assemble a demon harem, to which she calls you a fool and says that the other girls will rip you to shreds, but she'll tag along because she simply has to see it. Modeus joins the party and the player is greeted with a "SUCCESS" prompt, advancing on to Level 3.