Well, in 'gaster adopts a human fanfiction', it might start with the human character being in a world that is unfamiliar or dangerous. Gaster, who could be seen as a mysterious and powerful figure, notices the human. He might be intrigued by the human's nature or potential. So, he decides to adopt the human, which could lead to a series of events where the human has to adapt to Gaster's environment, learn about his ways, and perhaps they go on adventures together. It could also explore the relationship between the two, like how the human grows to trust Gaster and how Gaster comes to care for the human as a sort of parental or mentor - like figure.
In this fanfiction, perhaps the human is an outcast in their own world. Gaster, having his own reasons which could be related to some grand plan or just out of kindness, adopts the human. The story could involve the human discovering secrets about Gaster's past or the world they are now in. There might be other characters who react to this adoption, some being skeptical, others being curious. The human might also face challenges in terms of fitting in with Gaster's associates or dealing with any enemies that Gaster has. It could be a story full of mystery, growth, and new relationships.
Obviously, Gaster and the human are the main characters. Gaster is the one doing the adopting, and the human is the one being adopted.
Maybe a Pikachu adopts a human child. The Pikachu is part of a group of Pokemon that live near a human village. The child was abandoned, and the Pikachu takes it in. They go on adventures together, with the Pikachu protecting the child from other wild Pokemon and teaching it how to communicate with different Pokemon species.
A plot could be that Gaster has a connection to the Forbidden Forest in Harry Potter. He might be the source of some of the strange and dangerous creatures there. As Harry and his friends explore the forest more, they start to notice Gaster's influence. Gaster could also be using the forest as a way to try and get back to his own world or to gain power in the Harry Potter universe. This would lead to a series of adventures and battles as the characters try to either stop Gaster or understand his motives.
Well, it could be really interesting. Maybe Gaster would teach Naruto some unique and powerful magic or abilities that are different from the normal ninja skills in the Naruto world. Naruto might grow up with a very different perspective on power and friendship.
One possible plot could be that there is a rift in the multiverse which causes Danny Phantom to cross paths with Gaster. Gaster's knowledge of the multiverse and Danny's ability to traverse different dimensions in his ghost form could be combined. They start to explore the reasons behind this rift and discover that an evil entity is trying to merge different realities for its own malicious purposes. Danny and Gaster then have to use their unique skills to stop this entity and close the rift to restore the balance of their respective universes.
Well, it could be about Gaster suddenly reappearing in the lives of Sans and Papyrus. Maybe he has some important knowledge or a mission for them. For example, he might need their help to fix something in the Underground that's going wrong.
One common theme is the idea of family. The dragon and the human child form a unique family unit, often defying the norms of both their species. Another theme is acceptance. The dragon has to accept the human child as part of its life, and the child has to accept living with a dragon, which is a very different kind of existence.
One interesting story could be about a powerful wizard who adopts a human child with special powers. The wizard teaches the child magic and they go on adventures together. Another might be a story where an alien adopts a human child and tries to understand human culture while raising the child in a very different environment.
The storyline could involve Rarity introducing the human child to the world of Equestria. She might teach the child about fashion and elegance, as that's her forte. The child could also learn valuable lessons from Rarity's friends, like loyalty from Rainbow Dash or kindness from Fluttershy.
One common theme could be the exploration of their relationship in the context of the outertale universe. It might involve how they interact with the unique settings and other characters in that AU.