Because You Were Nice to Me

Sometimes redeemed villains or anti heroes is treated for the first time in their lives with genuine kindness and friendship from the main protagonist, friendship, love interest or family members.

Like for example: The Beast realize that Belle help him by healing his arm, because he save her from the wolves even though he done nothing, but being mean to her when they met. But Belle stay instead since she know that he have a good heart somewhere and not a monster.

It started with a Hero's Secret Past, Redeemed Villains and Enemies Turned Friends.

Here's why the heroes was being nice to anti-heroes or redeemed villains:
 * because they save their lives from danger
 * because they believe that they have goodness in their bitter heart (like Cindy Lou from the live action believe that Grinch is not mean, but misunderstood creature)
 * because they understand that the main antagonist (or his minions), monsters, love interest and anti-hero doesn't have any friends to talk with
 * because after they got along or see that people do care about their love ones (like Ash and Pikachu), the anti hero started to realize that they were wrong about heroes, humans or their arch enemies since there's goodness in their heart.

Examples

 * Iago in Aladdin: The Return of Jafar regrets helping Jafar after Aladdin sticks up for him and Aladdin and his friends treating Iago better than Jafar ever did. This causes his Heel–Face Turn and he ultimately helps them defeat Jafar.
 * Mew Two realize that Ash was right after seeing Pikachu and Ash really do care about each other, so he call off the fight
 * Cindy Lou Who from the live action believe that Mr. Grinch is not mean, but misunderstood after realizing that he have a tragic past and treat him with kindness.
 * Martha May Whoiver treat Grinch with kindness, because he made her a Christmas gift long time ago and have a secret crush on him like Grinch have a crush on her too.