Taiken

Taiken is the Slash ship between Ken Shiraishi and Taiga Kotaki from the Project SEKAI fandom.

Canon
Many years prior to the main Project SEKAI storyline, Ken and Taiga met in middle school. At first, Taiga found Ken boring, since he was more interested in getting a scholarship and doing sports. One day, Taiga asked Ken to get into street music, which he agreed to. In highschool, they formed the music group RADder with Nagi Kotaki, Taiga's sister.

Fanon
The ship is not very well known in the fandom due to some fans disliking Taiga or not paying attention to a lot of Vivid BAD SQUAD side characters. Nonetheless, the ship is still slightly popular on Twitter

Fandom
Kotaki Taiga/Ken Shiraishi tag on AO3.

Trivia

 * The ship is referred to with the 🐯🍵 emojis.
 * Taiga teases Ken a lot.
 * Akito mentions that Ken and Taiga's singing styles are 'polar opposites'.