I am looking for any movie or drama series where the main male lead gets rejected by the female lead at first. The heartbroken male then sets on his path to become a better person. He gets over the female lead and changes his previous self. And during this whole process, the female lead eventually falls in love with him.

I know the plot seems a bit too specific, but I wouldn't mind anything on the borderline. 

Also, I would appreciate if you could state a one line synopsis of the title you are mentioning.

Here are some borderline cases (all k-drama):

Reply 1997: Male lead doesn't necessarily get rejected but gives up in the beginning because his brother ends up asking the female lead for to be his girlfriend first. but he confesses later on and she has feelings for both and you'll have to watch it to the end to know who she'll end up with. Definitely a classic worth watching!

My Love Eun Dong: Female & male lead were a couple when they were younger, but then stuff happened and they were separated. male lead keeps looking for female lead and eventually finds her: married with a kid and apparently no memories of him. That doesn't stop him from trying to get them back together though. I loved this drama so much, especially the kids/teenage years!

It's Okay, That's Love: Male lead is the first to be interested in female lead, she is distant at first though, but they end up together. This drama doesn't have the "break" between characters (in which they don't see each other/male is not pursuing female) which you seem to be looking for. It's a great drama (great theme, characters, & plot), but, personally, I wouldn't watch it for the love-story. 

Hope this helps!
Hi My Sweetheart
When I See You Again
Both are Taiwanese dramas that fit your description.
cunning single lady 
she was pretty
i think these two fits 80% of you description. check it out. i enjoyed these ones hope you enjoy it too