When the rangers break the curse of Zen-Aku on Merrick, Princess Shayla is shown secretly searching for him. The relieved look on her face when she finds him is palpable, and she briefly allows herself to cradle his unconscious form for a moment before leaving so the other rangers can confront him. It's quite possibly one of the most loving, tender moments ever shown in the franchise.
When his best friend died in battle, he fell into a deep depression and lost faith in his comrades. She came to him in a vision, and after going against his worst enemies, he found a way to bring her back from the dead, taking her into his arms in joy. Sounds like perfectly flowery hero stuff, right? This is the villain'ssubplot.
A lot of Jindrax and Toxica's scenes are really sweet, really. Jindrax protects Toxica from the higher-up Orgs (when he can), and Toxica cheers up Jindrax when he starts getting down on himself. As mentioned before, this is all normal stuff for the Power Rangers. Seeing it happen with the villains is just...super sweet!
Another from Jindrax is how he shows a Big Brother Instinct when his sibling arrives in town. He even makes himself grow to giant size (something that Toxica doesn't want him to do) just so he can help his brother fight the Rangers.
The Crossover with Power Rangers Time Force reveals that Ransik and his daughter have both performed complete Heel Face Turns and found redemption. It gets even more so when Ransik destroys the Mut-Orgs mutant halves and is purged of his own, allowing him to live a normal life.
The end of the same crossover features all of both ranger teams, plus Ransik and Nadira, having a picnic, set to a remix of The Song of Animaria.
After witnessing some of Danny and Max's antics:
Eric: You've got some interesting friends. Taylor: They drive me crazy sometimes. Eric: I used to feel the same way about my friends.
While on a patrol together:
Cole: I never knew there were other Power Rangers. Wes: There's other Rangers out there, all right. We all fight for the same goal. Cole: It's nice to know there are others in this world like us. Wes: It's important to have friends you can count on.
Zen-Aku healed Alyssa rather than kill her, and even beat up other villains while doing so. This portrays him more of a Noble Demon rather than some generic villain overall.