Not best friend's little sister, but in Fight For My Way, ML falls for his best friend, who he considers like a sister or one of the guys, like he never saw her as a girl sort of thing before.
Reply 1994 - they are like siblings in relationship, and one of the dilemna of their relationship was that ML is considered a son to FLs family
Girls Generation 1979 - there is no sibling feelings, but the guy falls for the girl from the start, and later realizes she is the sister of his highschoolbestfriend
Foxy Lady - ML older sisters Bestfriend is the FL. So its more FL falling for her bestfriends younger bro
Hwarang - supporting couple, has guy fall for the girl who is sister to his childhood frenemy/rival
Revenge Note - its the storyline of the second male lead. FL ends up with someone else. But still a cute fluffy and enjoyable drama
Golden Pouch - ML and FL somehow becomes siblings at their adult age, then they fell for each other
Hwarang - supporting couple, has guy fall for the girl who is sister to his childhood frenemy/rival
Oh yeah, if you think about it Moo Myung / Sun Woo Rang did in fact fall in love for his best friend's sister, even if he laterpretended to be his best friend
