Fight My Way | The characters feel like a unit throughout the series, even before they officially get together. They were childhood friends and ML was FL's, first love. This is a wonderful series about understanding that dreams don't have to end because you grow up. It's about falling and standing back up with the support of those around you.
Come and Hug Me | This is a darker series but with tons of sweet moments between the characters. The leads are childhood sweethearts torn apart by the deeds of a serial killer. This series ends this week. Highly recommend it!
She was Pretty | The leads are childhood friends and each others' unspoken first love. They reunite as adults. ML starts being somewhat of a jerk but it gets a lot better.
Weightlifting Fairy Kim Bok Joo | Just a good feel series about childhood friends reuniting in university. The leads feel very natural together, so you can't help but see them as a couple even before they confess their feelings.