Mai Zen'in, younger twin sister of Maki Zen'in, belongs to the prestigious but oppressive Zen'in clan. Born into a family that devalued women and those with minimal jujutsu talent, both sisters endured systemic mistreatment. Unlike Maki who rebelled, Mai initially accepted a subservient role, preferring mundane chores over the violent life of a sorcerer. Maki's departure from the clan forced Mai into attending Kyoto Jujutsu High as a reluctant student, fueling deep resentment toward her sister for imposing this unwanted path. Her personality manifests as snarky, rude, and defensively crude, traits rooted in her traumatic upbringing and forced vocation. She frequently projects frustrations onto others, especially targeting Maki and Tokyo Jujutsu High students – taunting Maki's inability to use cursed energy and callously insulting Yuji Itadori shortly after his apparent death to provoke his friends. Despite this antagonism, she maintained functional relationships with Kyoto peers like Momo Nishimiya and Kasumi Miwa, and was one of the few who tolerated Aoi Todo's eccentricities. She expressed visible disappointment at Mechamaru's betrayal. Mai's bitterness toward Maki intensified over a broken childhood promise where Maki vowed to stay but left the clan alone. She concealed personal details from Maki, including her first crush and her latent cursed technique. After losing to Maki during the Goodwill Event, Mai questioned why her sister hadn't "fallen into the same hole" of resignation. Maki's unsatisfactory response perpetuated their estrangement. Graded as a level 3 sorcerer, Mai possessed minimal cursed energy and limited talent. Her primary skill was marksmanship, specializing in a cursed-energy-infused Colt Python revolver – firing rubber bullets in training and real bullets in combat. She demonstrated exceptional accuracy, incapacitating Nobara Kugisaki from a distance during the Goodwill Event and later sniping at Pseudo-Geto in Shibuya. Her innate technique, Construction, allowed materializing objects from cursed energy, but it was highly inefficient: creating a single bullet per day caused severe backlash like nosebleeds. This limitation, combined with her lack of physical prowess compared to Maki, underscored her combat vulnerability. Mai's arc culminated confronting their father, Ogi Zen'in, who mortally wounded both twins. Facing death, Mai sacrificed herself to save Maki. Using Construction for the final time, she forged the Split Soul Katana, a soul-severing weapon, and transferred all her remaining cursed energy to her sister. In this act, she acknowledged always holding Maki back and urged her to "destroy everything" – the Zen'in clan and its corrupt system. This sacrifice enabled Maki's transformation and power awakening, though Mai herself rejected the path of strength until the end, remaining faithful to her desire for a normal, nonviolent life. Outside jujutsu, Mai enjoyed caring for cacti, favored junk food, and avoided vegetarian dishes. Aoi Todo was a noted source of stress in her daily life. Her first love remains ambiguously cited as either Megumi Fushiguro or a stranger, with some unlikely speculation about Maki.