Lee Seung-Ryul should be insane by the fourth season, starts off as 20/21 years old (can't remember which it is). He's a very proficient striker, could easily make it in the EPL.
Johann Laureiro, DM with amazing skill with the ball at his feet. He can weave through the defense and hit long shots from 30 yards, he's class. At 18, he's our second best midfielder, and he'll soon be our best.
Rasmus Falk, AM, strangely great young player I stumbled across, can score well and plays like an experienced older player, with the speed and determination of a young player, all at the age of 19.
Kim Jin-Kyoo, DC, not sure how old he'll be (I think he starts as 25) but he's a rock at the back.
Kim Chi-Woo, DL/WBL, might be around 30 in your save. Solid, and has great running and passing skills. Also quite great at moving all the way up the wing and getting passes to wingers or crosses in.
Suk, amazing young ST, extremely great at scoring.
Ko Yo-Han, a great MC, can also play AMC, can play quite well sometimes.