Another good one could be 'The Bond Between Jack and Bunnymund'. It starts with a bit of conflict between them which then gradually turns into a deep emotional and romantic connection. The author does a great job of building the tension and the resolution in their relationship.
I'm not an expert on this, but often there could be themes related to the challenges of the unexpected pregnancy, like how the character deals with the physical and emotional changes. Another theme might be the reactions of the other characters in the story towards the mpreg situation.
One common theme is discovery. Often, the OC is new to the world of Bunnymund and has to discover how things work, like the magic and the rules of the Easter realm. For example, in many stories, the OC will be amazed at how Bunnymund can manipulate time and space for Easter egg hunts.
There's also 'The Wounded Bunnymund'. Here, Bunnymund is injured while protecting his territory from invaders. The author does an excellent job of describing his pain and the determination to recover. The fanfic delves into his internal struggle as he tries to regain his strength and also how his injury affects his relationship with other characters in the story.
Often, there are themes related to sacrifice. Bunnymund might get hurt while trying to protect someone or something important. And also, the theme of isolation can be present, where his being hurt leads to him being alone and having to deal with the pain on his own.
There's also 'Bunnymund: Guardian of the Hidden Realm'. This fanfic focuses on Bunnymund's role as a guardian. It has a great plot that involves him protecting his realm from various threats, and the way it portrays his determination and strength is really engaging.
In a world where Easter and a normal human world collided, the reader accidentally stumbled upon Bunnymund's lair. Bunnymund was startled but intrigued by the reader. As days passed, he showed the reader the magic of his Easter realm. The reader was amazed and in return, showed Bunnymund the beauty of human creativity. Their mutual admiration turned into love as they realized how much they complemented each other.
I really like 'The Bond of Winter and Spring' in the 'bunnymund x jack frost fanfiction' realm. It shows how Jack Frost's cool nature and Bunnymund's more earthy, warm - heartedness can complement each other. The story has some really touching moments where they start to understand each other on a deeper level.