This is based on opinion. Please don't list it on a work's trope example list.
Tear Jerker / Wedding Peach
In the manga, after one too many failures, Pluie disowns Jama-P and tries to kill him. Peach manages to save him, however, and Jama-P is so touched that he performs a Heel–Face Turn.
In the manga, Nocturne's backstory. She was a singer who was only able to sing with the aid of a magical bracelet. One of her 'friends' asked to try on the bracelet, then took it and backstabbed her. She lost her voice and her love, and then was approached to become a demon. Upon hearing this, the Love Angels try to redeem her instead of destroying her.
In Volume 2, a Brainwashed and Crazy Lily and Daisy tear into Momoko physically and mentally, but she stays strong and is able to snap them out of it.
Volume 4 of the manga has a bonus story where Momoko is approached by a demon impersonating her mother, Celestia. When she figures it out and tries to transform, she's unable to because of a barrier placed around her. The demon tells her she will be trapped there for eternity and her mother doesn't care about her, having left her lonely for so long. But Momoko gathers strength and her love for her mother, and is able to break through the barrier and transform.
After the demon is defeated, Celestia appears briefly to talk with Momoko, apologizing for leaving their family and affirming she loves her.
Volume 5's bonus story about Limone and Angel Lily, detailing their love and Limone's anguish when Lily is killed with the other Angels.
The emotional torment Momoko goes through after Yosuke becomes a demon. Salvia makes it worse by saying he's beyond help.
The anime has one for those who've read the manga. In the manga, Scarlett/Angel Salvia gets a boyfriend at the end. In the anime, her boyfriend was just using her and she ends up alone.