Another theme is the struggle between good and evil. The ocs can be faced with moral choices, whether to side with the more 'good' characters in Undertale or be tempted by the 'evil' forces. This adds depth to the story and makes it more interesting.
One common theme is self - discovery. The monster OCs often start out not really knowing who they are or what they can do, and then through their adventures in the Underground, they learn more about themselves. For example, they might discover hidden powers or a new purpose in life.
One common theme is self - discovery. The male OCs often have to figure out who they are in the context of the Underground world. For example, they might discover hidden powers or aspects of their personality. Another theme is friendship. They form bonds with the canon undertale characters, like befriending Sans or Papyrus.
One common theme is friendship. The OC often forms a strong bond with Sans, going through various adventures together. Another theme is self - discovery. The OC might be on a journey to find out who they are in the context of the Undertale world.
Another common theme is self - discovery. The OC, being a new character in the Undertale universe, often goes through a journey of self - discovery. Papyrus can play a role in this, either by being a guide or by being part of the situations that make the OC learn more about themselves. In some fanfictions, the OC discovers hidden powers or aspects of their personality while interacting with Papyrus.
One common theme is probably the exploration of relationships between male characters in the Undertale world. It could be about how they support each other and grow closer.
One common theme is the change in relationships. For example, how the character's partner or friends react to the pregnancy. Another theme is the anticipation and fear of the unknown. Since the Undertale world has its own unique elements, the pregnancy might bring new challenges and uncertainties. Also, the theme of protection often comes up, with the character and those around them being protective of the unborn.
One common theme is redemption. Many fanfics try to show Chara in a new light, as a character who can be redeemed despite her actions in the game. For example, they might explore her backstory to find reasons for her behavior and then show her growing and changing for the better.
Identity is also a big theme. The undertale characters are put in new situations in the supernatural crossovers, and they start to question who they really are. For instance, if Chara is exposed to a world of angels and demons in a crossover, they might wonder if they are truly a 'bad' character or if they can change and find a new purpose in this new and complex supernatural setting.
The exploration of morality is a theme that can be found. In Undertale, morality is a huge part of the gameplay with choices between mercy and killing. In BATIM, there are also moral dilemmas in a sense, like whether to trust certain characters or not. Fanfics might combine these moral aspects, having characters from both face new moral choices in the crossover world. Also, the theme of discovery is there, as characters discover the new rules and beings of the other's universe.
One common theme is redemption. Since Chara has some dark aspects in the game, many fanfics explore the idea of Chara being redeemed through their relationship with Sans. Another theme is friendship. Despite their differences, they can form an unlikely bond. And there's also the theme of mystery, as both characters have elements of mystery in the original game, and fanfics often expand on that.