Night Angels |Ninjago|

Kai a boy who had a "normal" life until a boy and transferred to his school the boy was very strange he was also very childlike looking like a child and they end up staying in the same dormitory In Kai's view this is the worst of the worst For the boy this is only part of his mission~
Who is this boy? What mission does he have to cover? What will happen to Kai? [I used base on the cover]