My Strange Hero.

When Kang Bok-Soo was a high school student, he was falsely accused of committing violence and kicked out of school. This was caused by his first love Son Soo-Jung and a male student Oh Se-Ho. Kang Bok-Soo is a now an adult, but his life has not gone smoothly. To get revenge on Son Soo-Jung and Oh Se-Ho, he returns to the same high school as a student. The environment at the school has changed and Kang Bok-Soo gets involved in unexpected cases.