The plot could be centered around the chaos that ensues when Itachi turns into a baby. His enemies might see this as an opportunity to attack, thinking he's vulnerable. However, his allies would protect him. And as they take care of him, they might discover new things about Itachi's past or even his true nature that was hidden before. There could be many comical scenes like when they try to diaper him or feed him baby food and he makes a fuss.
Perhaps in the fanfiction, Annabeth turning into a baby could be part of a magical curse. Her friends would then embark on a quest to find the antidote. Along the way, baby Annabeth could display some of her old characteristics in a cute, baby - like way. For instance, she might still show an interest in architecture by babbling when she sees grand buildings.
Obviously, Itachi as a baby would be a main character. Sasuke would also be a key character as Itachi's brother. Their relationship would be very different now that Itachi is a baby. Naruto could also be involved, perhaps being curious about this strange transformation and wanting to help out in some way.
In this fanfiction, Itachi might find a baby who is an orphan. He realizes the harsh reality of the world the baby will face without protection. He then becomes the baby's guardian, facing many challenges such as hiding the baby from his enemies and finding a safe place for the baby to grow up. He might also have to deal with his own internal conflicts about whether he is a suitable person to take care of a baby, considering his own past and the life he leads.
One possible plot could be that the magic backfires on Voldemort during a powerful dark spell. As a baby, he has no memory of his previous self. The wizarding world is in chaos as they don't know what to do with this baby - voldemort. Some might want to kill him immediately, while others think he could be redeemed. Harry Potter, having defeated him once, feels a strange sense of responsibility and wants to make sure he doesn't grow up to be evil again.
Well, one possible plot could be that his friends have to take care of him. They might struggle at first, not knowing how to handle a baby Izuku. For example, Bakugo could be really frustrated but gradually learn to be gentle. Ochaco might be really good at soothing baby Izuku when he cries.
The plot could be that Deku is doing some sort of experiment in the school lab when something goes wrong. A chemical reaction or a malfunctioning device causes him to turn into a baby. All Might hears about it and comes to visit. He feels a sense of responsibility as Deku is his successor. The other students are both amused and worried. They start to learn about taking care of a baby, like feeding, changing diapers, and making sure he sleeps well. Meanwhile, the teachers are researching how to reverse the transformation, and they suspect that it might be related to some ancient quirk theory that they need to dig deeper into.
One possible plot could be that a magic spell gone wrong in Berk turns Hiccup into a baby. Toothless, being his loyal friend, tries to protect the baby Hiccup from the chaos that ensues. The other Vikings are confused at first but then start to take care of the baby Hiccup in their own clumsy ways, leading to some comical situations.
Well, perhaps it could be about a magical event that causes Ash to transform into a baby. Then his friends have to take care of him while also trying to find a way to reverse the transformation. Maybe Pikachu has to protect baby Ash from other Pokémon who might mistake him for an easy target.
Maybe there's a new villain in the kingdom who has a device that can transform enemies into harmless forms, like turning Luigi into a baby. The villain wants to use this to stop Luigi and Mario from interfering with his evil plans. Mario has to protect baby Luigi from the villain's minions while looking for a way to break the transformation. This could involve exploring new areas of the kingdom and meeting new characters who might have the knowledge to reverse it.
Well, it could be that Edward is cursed by a powerful witch. The witch might be angry with him for some reason. And so, he turns into a baby. His friends then have to figure out how to break the curse while taking care of baby Edward. They might go on a journey to find a special herb or a magic item.