Choegoui Agdang

When Sawoo gets bullied in high school, his only friend Kido promises to teach him how to become the greatest villain. But Kido goes overseas after teaching Sawoo only two of the three rules. Faithfully following the two rules, Sawoo writes Kido many letters hoping he will get to learn the last remaining rule, but Kido never replies. One day after four years, Kido shows up in front of Sawoo, thinking those were love letters... (Source: Netcomics)