Love might be a theme. Whether it's romantic love, family love or the love between friends, it's a common and powerful theme in stories. For example, if it's a story about a character's journey to find true love, that would be a very engaging theme. And it could also be about self - discovery. The protagonist might go through a series of events that lead them to understand themselves better.
It could be about friendship. Many great stories revolve around the relationships between friends.
Another possible theme could be survival. If your story is set in a harsh environment, like a post - apocalyptic world or a deserted island, the theme of survival, with characters having to find food, shelter and deal with threats, can be very compelling. Also, the theme of redemption is possible. A character might have made mistakes in the past and is trying to make up for them throughout the story.