Is there a drama where the character is unwilling to exert any effort in their lives or has a careless attitude, or is a slacker good-for-nothing or anything somewhere around those themes? Thank you.

The ML is careless, reckless, rebellious, a womanizer and / or a slacker-good-for nothing of some kind, and changes after falling for the FL:

The FL doesn't excel in school in the beginning:

The FL is portrayed as a naive slob who lacks self-esteem and ambition in the beginning:

Maybe there dramas:

  • My Unfortunate Boyfriend
  • Hotaru no Hikari _normal in workplace but a doesnt have a care in her private life 
  • Clean With Passion For Now - slob
  • Age of Youth - jiwon is a carefree wild girl 
  • Ore no Hanashi wa Nagai
  • Flower for My Life