Elodie can become engaged to the also-recently-orphaned Adair, Duke of Elath. With enough skill in Animal Handling, they proceed to bond over frog-catching. If she instead leaves him in the custody of Arisse or Adele, he sends her a badly-written but heartfelt thank-you letter for letting him stay with his stepfamily (as opposed to the too-perfect dictated one she gets if she sends him to his grandfather). And she also gets a nice letter if she sends him to her uncle Armand, since there are a lot of frogs in Mazomba.
Early in the game, one of Elodie's optional weekend talks with her father begins with her just saying "I love you." She then starts thinking about how silly it is of her to interrupt his important work with her feelings, but then he hugs her and tells her he loves her too.
If Elodie saves the day with the power of music, Togami's children send her a drawing of a pink-haired angel.
The dude may be Ax-Crazy, but there's something heartwarming about marrying Kevan, the Earl of Io, and how he slowly opens up about his sexual abuse at the hands of his stepfather. It's suggested that the marriage ends up working out despite his issues.
Elodie's happy relationship with her cousin Charlotte is heartwarming in general. If you fail a check early on Charlotte pushes you out of the way and gets bitten by a snake; she likes you that much. Charlotte's sprites in conversation are almost always "happy" unless you kill her mother. And if you don't have a high Cruelty stat near the end of the game, and if you accidentally disturb the Kraken, you are offered an easy way out of sacrificing yourself; all you have to do is sacrifice someone of Lumen blood instead - and the only person fitting that criteria is Charlotte. Without a high Cruelty stat, though, Elodie flat-out refuses to do that to her "favorite cousin".
Elodie and Briony's oddly precocious, cute romance that ensues from barely surviving their trip into the old capital. Puppy love, yes, but the friendship lasts through the ages.
Actually, it's heavily implied despite being married to other people, that Elodie and Briory are still in-love with each other. Which is even more heartwarming.
A partial success in Decoration at the Festival of the Good Lady gets you this:
You hear the occasional little girl squeal "Pretty!" as you pass by, and can't hide your smile.
Added in the updates is an achievement for romancing and marrying a commoner. If you choose to go for this particular achievement you can get a very sweet little romance and epilogue. Evrard turn out to be Alice's brother, and runs into Elodie if her climbing skills are high enough and she catches him stealing apples in the gardens. One of the ways to get the achievement for marrying him requires keeping everyone happy, plus winning the naval battle later in the game or saving the day with the power of music. Most of the choices for this make Elodie into a strong and confident ruler, who avoids a lot of the dangers and political dramas of court life, and in the end marries one of the only characters in the game - except for Charlotte - who never tries to hurt or manipulate her. The game even notes that while their marriage has tongues wagging, it's a strong one and the two of them are very happy together. They even have three children together! D'awwww.