I'm looking for dramas that ML is a bad person at first, but has a good character development

These fit the bill. 

MLs used to be bullies in each of these (they are remakes):

Boys Over Flowers 
F4 Thailand: Boys Over Flowers 
Meteor Garden 

Husbands changing:

18 Again
Doctor Cha 

ML was uncaring:

Ghost Doctor 
Love Between Fairy and Devil 
Tale of the Nine-Tailed (second ML)
Till the End of the Moon 

There is one more but even the title would be a spoiler:

Mouse 

My girl 

During the drama, his character is influenced by the female lead (she is a nice and soft girl), and in the end you can notice he had become a better person because of her.