Twin-Ception

this is a fantastic of ninjago so basically ninjago gets attacked by a new person no one knew or even could tell who he is.. until Kai.. he knew who the person was.. as the person kept saving Kai and never let Kai get hurt also the same as nya the person also had powers that Kai knew who they were for. who is this person? how does Kai know this person? why does he keep saving the smith family?