MeiUi

MeiUi is the family ship between Mei Mei and Ui Ui from the Jujutsu Kaisen fandom.

Shibuya Incident Arc
On October 31, Ui Ui is with his sister and Yuji in Shibuya. When Mei Mei gets a call about a veil appearing, they head out to check up on it. Once they arrive at the Station, Ui Ui waits by an entrance while Mei Mei uses her power to spy on what is happening in the station. When Yuji gets impatient, Ui Ui tells him to calm down while his sister is checking out the station. Once Mei Mei is finished with her task, he listens as Mei Mei explains everything that is happening in the station. After listening to this, Ui Ui heads out with his sister while Yuji enters the station through a different entrance. When the curtain has been raised, Ui Ui informs his sister. The two then head to B5F platform to wait for Yuji.

Once Yuji arrives at their location, the three head off to where the trapped people are at which Ui Ui carries his sisters axe along the way. While running, Ui Ui gets angry at Yuji for not accepting his sister compliment. Once they arrive at the station, they notice that only one person is there. Ui Ui, along with Mei Mei and Yuji, then head towards Gojo's location, but stop when Yuji is suddenly contacted by Kokichi Muta. Ui Ui, Mei Mei and Yuji listen as Kokichi explains what is happening in Shibuya. Ui Ui decides to help his sister face off against the curse users while Yuji heads back to help Gojo.

Once the curse users get close enough, Mei Mei and Ui Ui prepare to fight. After the curse user's cursed spirit is defeated, Ui Ui watches as his sister defeats him as well. When Mei Mei defeats the other cursed users, Ui Ui informs his sister that the curtain has come down and the two head towards the station. After a while, Ui Ui and Mei Mei are confronted by Kenjaku. Ui Ui then watches as Mei Mei deals with the cursed spirit that Kenjaku had left them. When Mei Mei manages to figure out how Smallpox Deity's attack works, she asks Ui Ui to die for her which he agrees to. Smallpox Deity is exorcised and the siblings are released from his domain. Ui Ui and Mei Mei then prepare to face Kenjaku.

Ui Ui and Mei Mei are seen in a hotel room in Kuala Lumpur, Malaysia, having escaped Shibuya using Ui Ui's cursed technique.

Culling Game Arc
During the Culling Game, Ui Ui became affiliated with the students, and was used as the means of communication by group members because of his technique. Maki mentions that the two siblings are famous for scheming and Noritoshi replies that the siblings would call their associaton diversifying risk and making upfront investments.

Shinjuku Showdown Arc
Mei Mei uses her technique to stream Gojo's fight with Sukuna. Ui Ui prepares food for her crows.

Fanon
is a small ship within the Jujutsu Kaisen fandom as it only has 6 fanfictions written on Archive of our Own. It has a smaller popularity than other sibling relationships such as MakiMai or MeguMiki as neither Mei Mei or Ui Ui have the popularity Megumi or Maki have. Fans often use Mei Mei relationship with her brother as example of how unmoral she and other sorcerers can be. Mei Mei only values her family relationships because of the value they can bring to her, she has no issue asking her little brother to die for her. On the other hand, Ui Ui seems to dependent on his sister and greatly admires her. Making their relationship very unbalanced.

Fandom
FAN FICTION

Trivia

 * Because of a binding vow, Ui Ui can only use his technique if he has his sister's permission.
 * Ui Ui always finishes his plate when he's in front of his sister.
 * Ui Ui is stresses when he's not with his sister.
 * Ui Ui's talent/hobby is to organize Mei Mei schedule.
 * Both Mei Mei's and Ui Ui's favorite dishes are Malaysian: Bak kut teh and Pisang goreng respectively.
 * Mei Mei and Ui Ui do not have any other siblings.
 * Mei Mei is a pseudonym, it can be assumed the same for Ui Ui.