Subsequently, Kim Ji Yong begins living two entirely different lives. On weekdays, he's a model student at the police university. During the weekends, he punishes criminals who'd received light sentences and continue to commit criminal acts. Now called Vigilante, Ji Yong receives help from admirer Cho Kang Ok. Meanwhile, Detective Cho Heon chases after the man called Vigilante. (Source: AsianWiki; edited by MyDramaList)

Kim Ji Yong begins living two entirely different lives. On weekdays, he's a model student at the police university. During the weekends, he punishes criminals who'd received light sentences and continue to commit criminal acts. Now called Vigilante, Ji Yong receives help from admirer Cho Kang Ok. Meanwhile, Detective Cho Heon chases after the man called Vigilante.

(Source: AsianWiki; edited by MyDramaList)

They are both romance stories that include time travel.
The Plot of the stories are very similar.

Han Jun Hee's boyfriend Koo Yeon Jun died one year ago. She still hasn't gotten over his death and misses him a lot. One day, she somehow travels back in time to the year 1998 and finds herself as high school student Kwon Min Joo. There, she meets high school student Nam Si Heon. She is surprised to see how much Nam Si Heon resembles her late boyfriend Koo Yeon Jun. (Source: AsianWiki; edited by MyDramaList)