MitsuKouKasa

MitsuKouKasa is the poly ship between Mitsuba Sousuke, Minamoto Kou and Yugi Tsukasa from the Toilet-bound Hanako-kun fandom.

Canon
Mitsuba and Tsukasa were the first two of the three to meet each other off-camera. Mitsuba had supposedly summoned Tsukasa in need of a wish, and Tsukasa had offered to grant it for him. Mitsuba's wish was that he wanted friends, and then that is when Kou came along and he and Mitsuba met. Kou offered to help Mitsuba finish his unfinished business, and the pair walked around the school and took photos together. There is a moment where Kou tells Mitsuba that they can be friends even if Mitsuba is dead, and then Mitsuba takes a photo of him, responding that it was "something important to him" when questioned what he took a photo of by the blonde.

All three of the pair met shortly after that, where Tsukasa extracted part of Mitsuba's mind and soul in order to create a newer, better Mitsuba. Kou charges at Tsukasa and tells him to stop hurting Mitsuba, but this only results in Kou being knocked back.

The three meet again in the Hell of Mirrors Arc, where Tsukasa explains to Kou what he did to Mitsuba. Kou yet again gets angry and tries to fight Tsukasa, but before he can, he is accidentally knocked back by Mitsuba's scarf.

In the Picture Perfect Arc, Kou tells Mitsuba that he will "never let [him] go back to that guy," referring to Tsukasa. Mitsuba acts confused and asks him what he's talking about.

Fanon
The ship was popularized due to the dynamic of Kou, his vaguely implied love interest, and the person who took his vaguely implied love interest away from him. This ship currently only has 2+ works on AO3, therefore it is considered a rarepair. People normally tend to ship the aforementioned Mitsukou for Mitsuba and Kou, and TsukaSaku for Tsukasa.

Fandom
FAN FICTION

Variations
Mitsukou refers to the ship between Mitsuba and Kou TsuKou refers to the ship between Tsukasa and Kou TsuMitsu refers to the ship between Tsukasa and Mitsuba