How do you get jin in grandchase

You can either buy his worn-out mission or the cash mission from the academy tab.
If you have spent real life $$$ then buy the cash mission because you only need 1 crystal to finish it. While the worn out mission you have to clear The Whispering Woods and Ruins Of The Silver Knights on champion and get 5 treant logs(found from boss of The Whispering Woods 3 stars) and 5 black fairy powders(found from boss in Ruins of The Silver Knights). And be patient cause they don't always drop.