One common theme is the shock factor. When a usually slender character like Ciel or Sebastian suddenly gains weight, it causes a stir among the other characters. Another theme could be self - discovery. The character who gains weight might have to re - evaluate their self - image and how they interact with others.
Often, there are themes related to relationships. For instance, how a character's friends or romantic partner react to their weight gain. Some fanfictions show the support and love the character receives, while others might explore more complex or negative reactions. There can also be themes about self - discovery during the process of weight gain, where the character finds new aspects of themselves they didn't know before.
I'm not sure of specific 'Black Butler' weight gain fanfictions off the top of my head. But you could also try looking on FanFiction.net. You can use the search bar and type in 'Black Butler weight gain' and it'll show you relevant stories. Some might be more creative and interesting than others, like stories where Sebastian has to deal with a suddenly plump Ciel, which could lead to really unique plot developments.
Another theme is the reaction of other characters. In a lot of supernatural weight gain fanfiction, the friends or family of the character going through the change have different reactions. Some might be supportive, while others could be judgmental, adding an interesting layer of drama to the story. It also often involves the character having to adapt to new limitations or abilities that come with the weight gain, like in some cases, they might find they have increased strength but decreased mobility.
One common theme could be the exploration of a character's self - image during weight gain. In the context of Twilight, it might be how a vampire or a werewolf deals with a physical change like that. Another theme could be the reactions of other characters in the Twilight universe to the weight gain, like how Edward or Bella might respond to a friend or family member's change.
One common theme is the change in the Pokemon's lifestyle. For example, if a Pokemon starts living in a place with abundant food, it may gain weight. Another theme is how the trainer reacts to the Pokemon's weight gain, whether they are concerned or accepting.
Another theme is acceptance. In many such fanfictions, like 'A New Body for Him', the male has to come to terms with his new body and the way society views him. It's about learning to love oneself despite the changes.
One common theme is self - acceptance. Draco often has to come to terms with his new body and appearance, learning to love himself despite the changes. For example, in many stories, he starts off hating the weight gain but gradually realizes that his worth is not just based on his looks.
Another theme is the reaction of others. In weight gain stories fanfiction, the reactions of friends, family, and sometimes strangers can play a big role. Sometimes it's positive support, but other times it can be negative, which adds to the drama of the story.
One common theme is self - acceptance. The male character often has to come to terms with his new body shape and learn to love himself again. For example, he might initially be self - conscious but gradually realizes that his worth is not solely defined by his appearance.
Another theme is the impact on relationships. His relationships with other characters, whether it be with his colleagues or students, can change drastically. Sometimes it leads to new friendships or deeper understanding, while other times it causes friction.