RuiKasa

RuiKasa is the slash ship between Rui Kamishiro and Tsukasa Tenma from the Project SEKAI fandom.

Canon
Rui and Tsukasa are members of the unit Wonderlands x Showtime. They go to the same high school, and are well known as the "duo of weirdos" there.

Tsukasa and Rui first met during the Wonderlands x Showtime main story. Rui was telling a story and used robots to make the show more interesting, his performance Caught Tsukasa's and Emu's attention and Tsukasa thought that his performance was incredible, and that he would make a good director.

The day after, Tsukasa went to look for Rui around his school. After a while of looking for him and asking about him from his classmates, he was left with one more place to look for him - the roof. "only people on the rooftop at this time would be couples or weirdos…" he said, then Tsukasa found Rui on the roof and after Rui told him that he was watching him, Tsukasa asked him to perform shows with him, Rui said that it sounds interesting, and after a little convincing he agreed and him and Nene joined.

during Wonderlands x Showtime's first show, NeneRobo's battery ran out and they had to finish their show early. Tsukasa loses his temper and gets mad at Nene and Rui, Nene ran away and Rui told Tsukasa that he crossed the line, and that he cannot become a star. Tsukasa went to the Sekai, and talked to Kaito and Miku. He reflected on his actions and remembered that the reason that he wanted to become a star is to make his sister smile, And he decided that he will form Wonderlands x showtime again.

He got back to the real world and after he apologized and talked to Emu, they decided that they will make everyone smile and they went to look for Rui and Nene. After Tsukasa apologized to Nene she said that she wants to continue performing shows and all of them went to look for Rui. They found Rui telling one of his stories on the street, and when Rui saw them he finished the show. Tsukasa apologized to him but Rui didn't forgive him, and told him he doesn't to perform with him anymore. Emu encouraged him to keep trying and they got an idea.

Later that night, Emu Nene and Tsukasa found Rui and took him to the Sekai. when they got there Miku, Kaito and the rest started performing for Rui. When the show was about to end Tsukasa's name box changed from the character he was playing back to his name and he asked the alchemist to go back and preform shows with him again. Kaito asked Rui what he thinks the alchemist did and Rui told him that it's his role, and Kaito told him that he was merely a placeholder for him. Tsukasa told him that he wanted to convey his feelings to him through a show, and begged for him to perform shows with him. Rui laughed, and eventually agreed to join them again, and all of Wonderlands x Showtime got back to making shows.

Rui and Tsukasa became good friends after that and they hang out in their school very often. Tsukasa thinks that Rui is "awesome, but crazy" and Rui thinks that Tsukasa is "an actor worthy of a stage".

Fanon
RuiKasa is one of the most popular ships in the fandom, and has the most works for this fandom on AO3.

Fandom
FAN FICTION

Rui/Tsukasa tag on  AO3