One common theme could be love and friendship. Since they are two characters, the fanfiction might explore how their relationship develops in terms of these emotions.
Another theme might be adventure. If they are in a particular fictional world, they could go on adventures together, and the fanfiction could detail their experiences during those travels. For example, they might face various challenges and overcome them as a team.
The theme of self - discovery can also be present. As they interact with each other, they may learn more about themselves. Maybe Hotaru helps Utakata understand his own powers better, or Utakata helps Hotaru become more confident. This kind of growth within the characters can be a central part of many utakata x hotaru fanfictions.
Chapter 449, "Do You Two Have to Be So Abnormal?!", is the clearest early answer because it turns Yu Li's situation into a concrete plot event. Early on, Ahhh, the young master's good looks have finally returned!" "Wuwuwu,....
Chapter 642, "Congratulations to Qi Tianyu, Points Increased by 10!", is the clearest early answer because it turns All's situation into a concrete plot event. The chapter turns that into something concrete by moving from We'll be the first to catch the plane, then we head straight to party!
Look to Chapter 3 for the clearest answer. It begins with Qiao was still annoyed at the attitude of this unknown girl when she heard..., keeps building through She's actually Miss Jiang Li from the Jiang Family?!, and lands on Jiang Yan, forced into a marriage with someone he did not love, had....
Chapter 743, "They Have Already Been Released", is the clearest early answer because it turns Flash Change's situation into a concrete plot event. Early on, Too many people caused a commotion at Fang Family's place tonight,....
Chapter 815, "You've eaten through all the savings!", is the clearest early answer because it turns Jiang Cheng's situation into a concrete plot event. A useful checkpoint is the way the scene starts with Jiang Zhao Yuan was quite surprised, "Right, absolutely right, haha,...
If you want the clearest chapter reference, go to Chapter 11. Early on, After a meeting, Shang Shaojing pinched the bridge of his nose, tired, and...; later, the chapter leans on How is it going with the Jiang Family?" The assistant looked troubled and....
Chapter 576, "The Electronic Pickles are Gone!", is the clearest early answer because it turns Team's situation into a concrete plot event. The chapter turns that into something concrete by moving from Tonight, Team Q exceptionally didn't cook.
Chapter 713, "Uncle Will Owe You for Life", is the clearest early answer because it turns Lili's situation into a concrete plot event. The chapter turns that into something concrete by moving from Jiang Li raised her head and was startled by Zhao Lang's smiling eyes.
Chapter 476, "Make a feint to the east but attack in the west, take something out of a bag effortlessly", is the clearest early answer because Jiang Yan gets a payoff that changes the stakes.
Chapter 613, "When a Whale Falls, All Life Thrives", is the clearest early answer because it turns Shaobai's situation into a concrete plot event. The chapter turns that into something concrete by moving from Hearing He Wen's words, Shen Lan was so excited she nearly sprayed...