Hi, (:

As the title says..

I'd like anything like one of the heroes or the good side was formerly villain or from the bad side...
This main character's personality or identity must be really bad or simply evil in the past.

The character's current personality must be redeemed at the present, a good nature, changed from rehabilitation after maybe their capture, or from love, or from their own willingness to change to the better, or maybe even from interest in the good side.

I can't think of good examples so here's what comes to mind:
Bastard (HWANG Youngchan) has the protagonist <following's spoiler> originally just like his father, empathetic killer, before he gets conscience from traumatic events with his mother, then amnesia clouding those events, though he's still forced to play accomplice role at the story's start.

Kubera: One Last God (Currygom) has one main character originally, not necessary or particularly evil, but had a very brutal nature and cold personality, thought it was still not shown in the ongoing series, but affected by his loved one, he changes to a peaceful wannabe playful guy, though he's still forced to play villain role at the story's start.

Please feel free to share anything good that matches even if only one trait.

That's it. Thank you.

"Superior" fits your criterias I think

The webtoon Myojin Tales would fit. The title character begins as an evil character, but gradually changes.

Basara - The heroine is good from the beginning, but the hero changes dramatically. In the beginning, he has the heroine's entire family murdered.

Project Arms with the character Al Bowen

Black Cat has pretty much that premise

Currently getting my life together~ (unsuccessfully)

I'd like more recs.

By recommending this series, its a bit of a spoiler, but you may also want to look into Black Haze. MC is on the "good guy" side but has a mysterious past with the enemy that gets uncovered as the series progresses.

Edit: If you do read it, don't get put off buy the beginning art. I have never seen such a dramatic art improvement scenario and the series starting around chapter ~80 gets to be absolutely GORGEOUS. If you don't believe me, just click on the most recent chapters. I was put off at first so,,, yeah.

Currently getting my life together~ (unsuccessfully)

'bump UP