Can someone translate what was written on that door?

I think it means "package" based on Google search. Almost as if they were saying "here is your package"

Thank you~☆

I think it might also be related to positions in chess/board, because the body was found with a toy in hand that had letters similar to those written on the door.

Yes its related to the game Janggi which is Korean chess, that Seongrok taught to Jeoh in the first season. What I like is that Jeoh is not a pawn anymore, he is the king with Seongrok his loyal knight

Plastic bag, Google translate said.
Wicked!