I want a asian drama about bad/rude/arrogant or a criminal guy falls for a girl first time in his life and tries to change for her.  He regrets about past actions and becomes "good guy". Basically,I want a "character devolopment" drama.

Flower of Evil is just what you described. First episode was boring to me but it become so good that it's my favorite.
Terrius Behind me- not exactly a bad guy but he is hiding his spy identity while babysitting a single mothers' kids after she lost her husband. It was more of a rom-com but I loved it.
Scarlet Heart Ryeo- historical. Heartbreaking. The ML is known for his notorious ways but he slightly changes once he falls for the FL.
Bulgasal:Immortal Souls- ML has lived for thousands of years and is trying to find FL to kill her after she did something to him in the past. Lots of character development. Slow burn.
Tempted- ML is a bad boy (not a criminal) and is trying to seduce an innocent FL for his own thing.
Kill it- ML is a criminal, FL is a crime detective or something. Quite heartbreaking tho.
Healer- ML is also hiding his idenity and starts working with FL and acts all innocent when he really isn't.

  • My Roommate Is a Gumiho (SML)
  • +1 Flower of Evil
  • Love with Flaws
  • The Penthouse: War in Life
  • Just Between Lovers

Love better than immportality

There are many dramas that are like that.  "Flower of Evil" is definitely one  as is "Scarlet Heart: Ryeo". Lee Joon Gi is ML in both. Most of the dramas are arrogant bad boy MLs who fall for the FL. It depends on how bad or aloof you want them to be.Try  "Boys over Flowers", "Meteor Garden", "Master Devil Please Don't Kiss Me Seasons 1 and 2". Read the synopsis  of any and they will tell you what you are looking for.  Personally I would ei her go through the MyDramaList or go to Vikki where you can read about the story line and get to choose. One does come to mind and that is "The King's Woman" But , most start off where the ML is arrogant and bad but there is always a story as to why. I hope you search these places and I guarantee you will find what you are looking for because it depends on your personal taste and what you consider Bad and the era /genre as well. Good Luck and Happy watching.

Ugly Duckling Series: Don't is a Thai drama where the "good girl" tames the "bad boy" or you can say that the "bad boy" changes for good for her.