Never_Not_Tam_Song
Kai was only 17 when he realized no on truly needed him anymore. He'd spent his life until then raising Nya and keeping her safe, then taking Lloyd Garmadon in, protecting Ninjago, almost dying...
The usual teenage activities.
Then his parents returned, Nya grew up, Lloyd became the Ultimate Spinjitzu Master, and peace spread over Ninjago.
So....what was Kai supposed to do now that he was of no use?