In fanfic, baby Luffy is often depicted as extremely curious. He's always eager to explore his surroundings, whether it's the small village on Dawn Island or the beach. His curiosity is so strong that it sometimes gets him into trouble, but he doesn't seem to mind.
It's possible that the baby's parents are from a rival pirate crew. In the 'luffy finds a baby fanfiction', this could lead to a lot of drama as Luffy has to decide whether to return the baby to its potentially dangerous family or keep it safe with his own crew. Or perhaps the baby's parents were victims of a powerful and evil force, and Luffy feels compelled to protect the baby from the same fate.
One common theme is mentorship. Whitebeard often takes on the role of a mentor to baby Luffy, teaching him about the pirate world. Another theme is family. The Whitebeard pirates are known for their strong sense of family, and with baby Luffy there, it emphasizes this aspect even more.
Shanks influences baby Luffy by being a role model. He shows Luffy the exciting life of a pirate. For example, his tales of adventure on the high seas make Luffy long for the same. Also, Shanks' courage, like when he faces danger without hesitation, makes Luffy admire him and want to be like him.
One possible plot could be that Luffy and Nami accidentally end up taking care of a baby during one of their adventures. Maybe they find the baby on an island they land on. Luffy, being his carefree self at first, tries to play with the baby like it's a new crewmate. Nami, on the other hand, is more practical and starts looking for supplies to take care of the baby. They face challenges like finding proper food for the baby and protecting it from other pirates or threats on the island.
The Marines could be antagonists. They might see the baby as a threat or something that needs to be taken away from Luffy and Nami's crew. Maybe they think the baby has some connection to a dangerous pirate or revolutionary. The Marines would try to capture the baby and arrest Luffy and Nami for having it.
In this fanfiction, perhaps Luffy might take on the role of a protector. He could be very confused at first, not knowing how to handle a baby. But then, his kind heart would lead him to try his best to keep the baby safe and find its family.
Zoro would be an interesting character to pair with them. He could act as a protector. With his strong swordsmanship, he can fend off any threats while baby Luffy is exploring and Law is doing his medical research or whatever he is occupied with. Zoro's serious nature would also create a nice contrast to Luffy's innocent playfulness and Law's more calculating personality.
One interesting plot could be baby Luffy getting lost on an island and Law, being the smart and capable one, finding him. They then form an unexpected friendship and go on little adventures together on the island, like exploring a mysterious cave filled with strange creatures.
There are 'baby Luffy and Whitebeard' fanfictions that might focus on a special bond. For instance, baby Luffy might be the only one able to make Whitebeard laugh with his silly antics. The fanfiction could develop a relationship where Whitebeard becomes like a grandfather figure to Luffy, guiding him in a way that's different from what he'll learn later in his journey. It could also show how Luffy's presence brings a new sense of family to the Whitebeard pirates.