Well, one possible theme could be about acceptance. Perhaps in the fanfic, Candy and Cindy come from different backgrounds or have different personalities, and the story is about how they accept each other's differences and become closer because of it. Or it could be a story of redemption, where one of them has made a mistake in the past and the other helps them to make amends and move forward in a positive way.
One common theme could be friendship. They might start as friends and then develop a deeper connection. Another could be adventure, where they go on some sort of journey together.
One common theme is friendship. Dipper and Candy often start as friends and the fanfic may explore how that friendship deepens. For example, they might support each other through tough times in Gravity Falls.
Another theme could be self - discovery. As they interact with each other, both Candy and Dipper may learn more about themselves. They might overcome their fears or find new talents while being with each other. This adds depth to the characters and the story as a whole.
I'm sorry, I don't have specific 'candy x cindy fanfic' to recommend directly. You can try searching on fanfic websites like Archive of Our Own. They usually have a large collection of various fanfictions.
One common theme could be self - discovery. Cindy might be on a journey to find out more about herself, her powers (if she has any in the story), or her place in the world.
Romance is also quite prevalent. Many fanfictions focus on the two characters falling in love, with all the typical romantic tropes like first kisses and confessions of love. They might write about how their relationship overcomes obstacles in their world.
One common theme is friendship turning into love. They start as comrades and then feelings develop.
Some common themes could be the battle between good and evil, as is typical in the Supernatural universe. There might also be themes of family, loyalty, and sacrifice. The characters often face difficult choices that test their moral compass.
A sense of wonder and discovery is often a theme. Cindy Lou might discover new things about the world from The Grinch, like the beauty in the mountains where he lives. And The Grinch can discover the warmth of community through Cindy Lou and the Whos. This exchange of new experiences between them is a popular theme in such fanfictions.
Redemption is a common theme. The Grinch is usually a grumpy and somewhat villainous character at first, but through his relationship with Cindy Lou, he finds a path to redemption. For example, in many fanfictions, he starts to see the beauty in Christmas and in the Whoville community.