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.
Easter eggs are related to the Easter story as they represent new life. Just as Jesus was resurrected, the egg is a symbol of new beginnings. It's a simple yet powerful connection.
The eggs themselves can be seen as an Easter egg in the Easter story. Eggs have long been associated with new life, which ties in perfectly with the theme of the resurrection in the Easter story. In many cultures, eggs are decorated during Easter to celebrate this new life aspect.
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.