Ilulu is a female dragon originally aligned with the Chaos Faction, marked by initial hostility toward human-dragon coexistence. Her past includes a traumatic childhood where she played with human children before witnessing her parents killed in a human attack. Fellow Chaos dragons then indoctrinated her into believing all humans were inherently evil, fostering deep-seated resentment despite lingering doubts.

In human form, she appears petite at 130cm tall, with pink slit-pupiled eyes and matching pink hair styled in low curly twin tails (featuring purple highlights in anime adaptations), alongside disproportionately large breasts. Her initial outfit was a black cloak with white fur and minimal undergarments; later, after joining Kobayashi's household, she adopted oversized t-shirts, thigh-high socks, and red shoes. While her full dragon form remains unseen, a "fun-sized" version depicts her wingless, with flame-like fur, a narrow snout, and distinctive horns. Her human form measurements are B130/W55/H70.

Personality development shows significant evolution. Initially destructive, war-mongering, and holding psychotic disdain for humanity, her defeat by Tohru and subsequent rescue by Kobayashi from the Harmony dragon Clemene catalyzed profound change. This shifted her toward a more laid-back yet socially awkward demeanor, often exhibiting childlike curiosity and emotional honesty. Early traits included shamelessness regarding nudity and impulsiveness, though she gradually developed human-like modesty, particularly around Taketo, and expressed guilt over past destructive intentions.

Her story arc began by targeting Tohru for coexisting with Kobayashi, leading to aerial battles where her power proved slightly below Tohru's. Subsequent attempts to sabotage Kobayashi and Tohru's relationship involved manipulating Kanna and magically transforming Kobayashi into male anatomy to provoke lustful reactions. After Clemene nearly killed her, Kobayashi's selfless intervention caused Ilulu to question her beliefs. She moved into Kobayashi's apartment as a third dragon resident, struggling to adapt to human society under Tohru's guidance. Seeking purpose, she took a job at a candy shop run by Taketo Aida's grandmother, developing romantic feelings for Taketo marked by increasing shyness, fear of rejection over her dragon identity, and protective instincts.

Her abilities center on fire manipulation: producing combustible "flame acid," requiring external heat sources like open flames to recharge, and immense physical strength capable of wounding Tohru. Additional powers include shapeshifting (initially flawed, resulting in dragon-like arms or fingerless nubs before mastery), gender transformation magic (used temporarily on Kobayashi), pyrokinesis, and draining portal creation. Her breasts function as "flame sacs," visibly glowing during fire attacks.

Relationships form key development markers. Kobayashi became a primary attachment figure whom Ilulu initially wished to "mate" with before redirecting affection. Taketo Aida emerged as her romantic interest, with interactions showing progression from teasing to mutual care and emotional vulnerability. Kanna Kamui serves as a peer-like friend for playful activities, while Elma transitions from rival to shopping companion. Lingering trauma from parental loss and forced ideological conformity underlies her interactions.

Spin-off media appearances include "Kanna's Daily Life," "Elma's Office Lady Diary," featuring clothing-shopping experiences with Elma, and the dedicated series "Ilulu Has No Clue About Love!," focusing on her candy store experiences and evolving relationship with Taketo.