he became a better person for her

any kdramas where the guy is mean or a bad guy, but then meets a nice and bubbly girl that makes him a better person.

Flower of Evil this is the best example in my list.

Ra Raerng Fai except the FL is not bubbly, she's a mature business lady.

Jealousy Incarnate he's an insufferable jerk but gets humbled by love

Oh My Ghost Pretty much the same kind of character (much milder though) but in a different setting

Loving, Never Forgetting He gets cured of his bitterness by the saintly FL (she's the exact opposite of bubbly, but she's nice).

Que Sera, Sera She's bubbly and nice, he's a player and a jerk. He figures out that his lifestyle is not giving him happiness, he does change but it's not really because of her.

Roy Leh Sanae Rai a player and a scoundrel gets whipped into shape by his saintly FL. At some point I felt sorry for the guy

I wouldn't use "bubbly" to describe these FLs, but the FL is good and the ML becomes a better person after meeting her:

• The Smile Has Left Your Eyes
• Something About 1 Percent
• Tempted
• 100 Days My Prince
• Falling for Innocence
• Marriage Contract
• Moon Lovers: Scarlet Heart Ryeo
• Secret
• Cheese in the Trap

Same note above applies for some of the FLs in these dramas, and the MLs also weren't exactly mean or bad, but they were either a bit rude and out of touch, very isolated + didn't care about other people, a bit rough around the edges or on a bad path and the FL helped them become better versions of themselves:

• Just Between Lovers
• Thirty But Seventeen
• School 2017
• I'm Not a Robot
• The Beauty Inside
• The Secret Life of My Secretary