Izuko Gaen cuts a distinctive figure: a middle-aged woman with wavy long brown hair, orange eyes, and vibrant hip-hop-inspired clothing. Her typical outfit features a loose light green shirt over a black sweatshirt, maroon pants, running shoes, a white baseball cap with a light green rim, a smiley necklace, and orange headphones around her neck. A swirl of rainbow clouds often manifests in the background around her. She commands a network of oddity specialists, primarily former members of the Occult Research Club she led in college, where she was the upperclassman of Meme Oshino, Yozuru Kagenui, and Deishuu Kaiki. Her role in creating the artificial oddity Yotsugi Ononoki resulted in a curse compelling her to "know everything," a condition she frequently references with her catchphrase: "There is nothing that I don't know. I know everything." She leverages this vast knowledge to manipulate situations and undermine confidence, as seen with Tsubasa Hanekawa. She is the sister of Tooe Gaen and aunt of Suruga Kanbaru. Gaen operates under a unique compensation system, demanding "friendship" – future favors owed – instead of immediate payment. This builds a network of indebted individuals. She maintains five cellphones and provided three contact numbers to Koyomi Araragi during their initial encounters. Strategically orchestrating key events, Gaen advised Mayoi Hachikuji and Koyomi Araragi in Shinobu Time that escaping the "darkness" required Mayoi reverting to her original "lost cow" form or passing on; Mayoi chose the latter. During Ougi Dark, she coordinated the confrontation against Ougi Oshino, revealing Ougi as a manifestation of Koyomi's subconscious. Her original plan involved installing Shinobu as the god of North Shirahebi Shrine, but she adapted when Koyomi returned from hell with Mayoi Hachikuji, designating Mayoi as the new deity due to the symbiotic relationship between slugs and snakes. This resurrection allowed Mayoi to exist without being consumed by the "darkness." After Ougi's defeat, Gaen complied with Shinobu's request to strip her powers and return her to Koyomi's shadow. In Hitagi End, she attempted to bribe Deishuu Kaiki via Yotsugi Ononoki to abandon Hitagi Senjougahara's request concerning Nadeko Sengoku. Though Kaiki accepted payment before reneging, it was implied Gaen anticipated this outcome. Her foresight was further shown in Yotsugi Doll, texting Koyomi a meeting location for Yozuru Kagenui before he requested assistance. Gaen wields two specialized swords: Kokorowatari, which kills any supernatural being with a single scratch, and Yumewatari, which reverses damage to such beings, including resurrection. Her abilities extend to interacting with non-corporeal entities like the ghost Mayoi Hachikuji and detecting deception. Despite her manipulative nature, she expresses a desire for deeper trust, notably wishing she could lend her prized cellphone to someone.