You're an error in my perfect world. 
 
Sang-U Chu is a stickler for rules. So when his classmates free-ride on a group project, he doesn't credit them. But this prevents one senior, Jae-Yeong Jang, from graduating. And like oil and water, Sang-U and Jae-Yeong don't mix. Can Sang-U debug Jae-Yeong — a semantic error in his perfect life? 
 
(Source: Manta, edited)
 
Note: Chapter count includes a Christmas Special.

Short ONA animating sweet moments from the novel and a new side story.