Choo Sang-woo, a Computer Science major, is a stickler for principles and the embodiment of rule compliance. The encounter between two individuals, one with a mind for engineering and the other for the arts, whose personalities don’t overlap in the slightest, continues relentlessly – whether by coincidence or fate. And somehow, despite everything, they are creating a mobile game together?! The bright red semantic error, Jang Jae-young, shakes Sang-woo's perfect world! Will he be able to debug this error?