The story begin with an invasion happen in a city of Japan where there is a dimension gate appear and alien come out , then they start to fight back.... and then the MC appear as a silver hair Boy with S rank power,that no body know where he's from then he joined a nerd guy with little power as a team to enter the academy/squad to fight back the alien and they go through tournament to select the team to go to the other side of the gate.....can't not remember the name of the character but i'm pretty sure the silver hair boy name is one word.

World Trigger?

~4400 manga completed
~1700 ongoing...