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 high school, they formed the music group RADder with Nagi Kotaki, Taiga's little sister.

Fanon
The ship is not very well known in the fandom due to some fans disliking Taiga, not paying attention to a lot of Vivid BAD SQUAD side characters, and due to the fact that Ken is already married. 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. Ken being represented by the Tea emoji because he owns WEEKEND GARAGE, a live music cafe, and Taiga being the tiger emoji because in the 4koma that came out alongside the Kick It Up a Notch event he is portrayed as a tiger wearing shades..
 * Taiga teases Ken a lot.
 * Both made questionable fashion choices when they were younger, Taiga wearing ugly Hawaiian shirts to important gigs and Ken wore socks with little cream sodas embroidered onto them to shows. The two of them poke fun at each other because of this in An’s second card story for her card in The Vivid Old Tale event,
 * The only time Ken is ever shown to be flustered in the game is when Taiga teases him. Normally he is composed, cool, and calm.
 * Akito mentions that Ken and Taiga's singing styles are 'polar opposites'. Ken’s style of singing is calm, whilst Taiga’s is overwhelming and powerful.
 * Both Ken and Taiga mentor members of Vivid BAD SQUAD. Ken mentors Akito in the Burn My Soul event, and Taiga mentors Kohane from the Bout For Beside You event up until the On Your Feet event
 * Ken and Taiga appear in 4koma #71 “The Faces of the New Generation” together.