Who is Mei Mei’s little brother in ‘Jujutsu Kaisen?’ Ui Ui and his cursed technique explained

Warning: Spoilers for the fight at the start of season 2 until episode 14

The Shibuya Incident puts many of our favorite Jujutsu Kaisen characters in some of the highest stakes circumstances they have ever been in thus far, especially those who are undergoing a possible promotion to First Grade.

That being said, although the arc mostly includes both sorcerers and curses we have grown to know in season 1, it also introduces a few new characters. One of these new characters we meet during the latter part of season 2 is First Grade sorcerer Mei Mei’s little brother Ui Ui, who has to be the youngest human sorcerer to be stepping inside the veils and partaking in the events of the Shibuya Incident Arc.

Introducing Ui Ui

Ui Ui first appears in season 2, episode 8 — the 32nd overall — or chapter 83 of Gege Akutami’s manga. When he’s introduced, he’s with Mei Mei and Yuji Itadori at Aoyama Cemetery, prior to them entering Meiji-Jingumae Station. From the get-go we see that he has a bit of an obsession over his elder sister, seemingly content in doing her every bidding, even going to the extent of laying a handkerchief down for her to sit without her having to ask him to. Ui Ui is as devoted to his older sibling as Mei Mei is motivated by money.

The way he acts and views Mei Mei is reminiscent of how Yushiro behaves around Lady Tamayo in the Demon Slayer series, also bearing the characteristic of being far more unpleasant to other characters — the protagonists in both instances — than to the object of their undying admiration. Not only is Ui Ui rude to Yuji, but he’s also disdainful of someone like Satoru Gojo for “forcing” his sister to be his backup. When Mei Mei tells him that the special-grade sorcerer shouldn’t be treated “like some ordinary man,” Ui Ui protests that she’s not ordinary either. He’s also seemingly unbothered by the fact that his sister values money, or “work relationships,” more so than family.

Ui Ui is voiced in Japanese by voice actress Yuko Sanpei, a professional in the industry since the year 2000 who has a generous repertoire of male roles under her belt, including anime protagonists such as Boruto Uzumaki, Taichi Yagami, and Tsubasa Ozora. In English, he is voiced by Sarah Anne Williams, who’s been active in the anime voice-acting industry since the early 2010s. She’s played characters like Sayaka Miki from Madoka Magica, Rika Shinozaki from the Sword Art Online series, Neferpitou from Hunter x Hunter, and Mirai Sarutobi from the Boruto series, among others.

Ui Ui’s cursed technique

Ui Ui’s cursed technique is showcased for the first time in season 2, episode 14. Before the opening song even plays, Mei Mei battles and defeats the Smallpox curse pseudo-Geto threw her way. It could be said that she emerges victorious and relatively unscathed thanks to her little brother’s assistance. Due to the scene’s fast pace — since Gojo’s sealing, this whole arc can be considered fast-paced — it might be hard for those watching the anime for the first time to understand what cursed technique Ui Ui used, how he managed not to die, and what his role truly is in tagging along with his first-grade sister.

At first, it appears like Mei Mei is just going to follow the coldest of logics and use her little brother as a sacrificial pawn in order to defeat their opponent. But that was mainly to throw viewers — and manga readers before them — for a loop. Her asking Ui Ui whether he’d die for her, was more of a: “Will you risk your life for me?” Knowing full well what her younger sibling’s cursed technique is, she must’ve been aware that he wouldn’t necessarily have to die in order for her to get a hit in.

Ui Ui possesses a Binding Vow with Mei Mei where she’s the one who permits him to use his jujutsu, as she does in this episode. Before being put in a coffin, the younger sibling shows that he has good control over his cursed energy and its output, successfully attracting the special-grade curse’s attention. Then, he uses New Shadow Style: Simple Domain, an anti-domain technique that we’d seen in action earlier this season when Kokichi Muta (aka Mechamaru) fights Mahito, finding a way out of Self-Embodiment of Perfection by using his classmate Kasumi Miwa’s technique. This technique serves as a counter to the Domain Expansion’s guaranteed hit feature. Thus, Ui Ui is able to avoid being squashed by a massive gravestone.

In addition, Ui Ui has an innate technique that hasn’t yet been revealed as of season 2, episode 14.