The plot could center around the mystery of how Ciel turned into a baby demon. There could be a search for a way to reverse it. His allies, like the Phantomhive servants, would be in a tizzy trying to keep him safe and figure out what happened. Ciel himself, despite being a baby, might still have some of his old memories and try to communicate in his own baby - like way, which could be really cute yet frustrating for those around him.
Well, one possible plot could be that the other characters in the story are initially shocked. Papyrus might be super confused but also determined to take care of his 'baby' brother. They could go on little adventures where Papyrus has to protect Sans from various threats in the Underground while also trying to figure out how to turn him back to normal.
One possible plot could be that the magic in the world goes haywire. Natsu is caught in a spell that turns him into a baby. His friends in Fairy Tail are shocked at first. Lucy might take on the role of a caretaker, trying to figure out how to reverse the spell while also dealing with a baby Natsu's unpredictable behavior like randomly using small bursts of fire magic that are more like cute little puffs now.
Well, the plot could involve his teammates having to take care of him. They might struggle at first because Kuroko as a baby can't communicate in the same way. Maybe they have to figure out his needs like when he's hungry or sleepy. And they could also try to keep it a secret from the other teams to avoid any distractions during games.
The story could start with some sort of strange experiment gone wrong that turns Junkrat into a baby. The rest of the crew is shocked at first. Mei could use her scientific knowledge to try and find a way to reverse the process. Meanwhile, Reinhardt might tell stories to baby Junkrat about their adventures, as if he can understand. And Lucio could play some soft music to keep the baby calm.
In this fanfiction, it could be that a powerful force in the underworld wants to see what would happen if a human and a demon had a child. So, it manipulates events to make Ciel pregnant. Ciel and Sebastian would initially be shocked but then gradually accept the situation. The story could detail how Sebastian protects Ciel during the pregnancy, how they prepare for the baby's arrival, and how they raise the child in a world that is not so accepting of their unique family situation. It could also show the growth of their relationship as they face this new chapter in their lives together.
In a 'ciel and lizzy having a baby fanfiction', perhaps the story could focus on how they first find out about the pregnancy. It could be a moment of shock and then joy. They start making plans for the baby's future right away. Ciel might start thinking about how to protect his family better, and Lizzy could be thinking about the kind of upbringing she wants for the child. Their relationship could also deepen as they go through this new phase in their lives.
In a 'ciel turns into a cat' fanfic, the story could start with Ciel waking up one day as a cat. He's confused and frustrated at first. But then he realizes that he can now explore places he couldn't before in his human form. He might end up befriending a group of street cats who teach him how to survive as a cat. Meanwhile, his servants are desperately searching for him, not realizing that he's the little cat they keep seeing around the manor.
Well, one possible plot could be that Jimmy's latest experiment goes wrong and he is turned into a baby. His friends, like Carl and Sheen, would be really confused at first. They might try to figure out how to reverse the process. Meanwhile, Jimmy as a baby would still have his super - intelligent mind, but be limited by his baby body. So he could be using baby - like actions to communicate his scientific ideas to his friends, like babbling and pointing at things he needs for a new experiment to reverse his condition.
In this fanfiction, it could be that a magical accident occurs during a potion - making class. Harry accidentally drinks a wrong potion which transforms him into a baby. Dumbledore then decides to keep Harry at Hogwarts, with the teachers taking turns to look after him. Meanwhile, Neville could be the one who discovers a clue about how to reverse the transformation by observing some strange behavior of magical plants in the school's greenhouse.
One possible plot could be that Sirius accidentally casts a spell that turns Harry into a baby. He then has to take care of Harry in this new form while trying to find a way to reverse the spell. He might face challenges like hiding Harry from the wrong people, and also dealing with Harry's baby - like needs such as feeding and changing diapers.