WARNING: UNMARKED SPOILERS FOR THE LIGHT NOVELS AND MANGA!
Patrick. He's, by all accounts, just an ordinary noble, but his determination to befriend (and maybe be more) with Yumiella is beautiful. Yumiella, in turn, becomes more emotional and open thanks to Patrick, and doesn't flee the country like she originally planned because of him.
Eleonora just being a bubbly, sweet girl who wants nothing more than to daydream about the boy he has a crush on. She doesn't have a mean bone in her body, and ends up taking a liking to Yumiella because she's always truthful to her, even if it's harsh.
Yumiella becoming a "mommy" to Ryu. Because newborn dragons recognize the being that fed them the most magic while in their eggs, Yumiella's level 99 magic means that Ryu has become a lovable, playful pet.
It works both ways as well; because of her intense dark magic, all other animals (and Alicia) see her as a black, ominous cloud. Ryu is literally the only animal Yumiella can interact with normally, and so she and Ryu immediately develop a special bond.
Unlike her counterpart in the light novels, anime Alicia doesn't grow to despise Yumiella or wish to kill her. While she's still traumatized by the dark dungeon, she's actually grateful to Yumiella for helping her level up, and even gives her one of her "heroine smiles".
Yumiella's finding out Patrick has been level-grinding to meet her (made-up) condition so he can court her. She creates a loophole that allows him to meet it, followed by them having their first kiss.
Yumiella's interactions with Phil, the young boy with dark-brown hair. Seeing him being mistreated over having darker hair moves Yumiella to become the new Count Dolkness and change everyone's perception of dark-haired people by ruling it fairly and wisely.
And she ends up doing so, with many of the Dolkness County villages rising from poverty thanks to her efforts. She even attains a loyal (albeit strange) following because of her adventures in the mountains as a child saving villages from monsters.
Yumiella crying while burying the Demon Lord's remains. The fact that she gets upset over having to kill him (her first human kill, by the way) proves that she truly is a good person at heart. Points to Patrick for comforting her while she mourned.
Patrick declaring that he will go with Yumiella to the Dolkness County. Granted, he's keeping an eye on her so she doesn't start any trouble, but Yumiella is just happy that he'll be by her side even after they graduate.
Yumiella's utter glee when she finds out Patrick is level 99. Of course she misses the fact that his "level 99 celebration" party will actually be their wedding, but it's the thought that counts.
