Well, perhaps they could become friends quickly. Bill might introduce Harry to some interesting magical things he hasn't seen before, like some unique creatures. And they could start having little adventures together around the wizarding world.
They might start as a sort of mentor - mentee relationship. Bill, being more experienced, can guide Harry in the wizarding world. As time passes, they could become like brothers, always having each other's backs.
They could be like brothers. Harry has a strong connection with the Weasley family already, and with Bill and Charlie, it could be a natural extension of that. They might look out for each other and support one another in any difficult situation.
Well, perhaps they could go on an adventure together. Maybe they discover a hidden magical place in the Forbidden Forest. They might use their combined skills, Harry's courage, Bill's experience with magical creatures, and Charlie's knowledge of dragons to overcome some sort of danger or mystery.
In this fanfiction, perhaps Harry will be initially hesitant and quiet when meeting Bill and Charlie. He might be in awe of their more experienced and confident personas. Bill could offer Harry some words of wisdom regarding the wizarding world outside of Hogwarts. Charlie, on the other hand, might share stories about dragons which would both fascinate and intimidate Harry.
In a 'Percy meets Triton at a young age' fanfiction, it could start with Percy being bullied at the beach. He runs into the water to get away from the bullies. Triton, who is observing from afar, is intrigued by Percy's quick thinking to use the water as an escape. Triton approaches Percy and offers to give him the ability to breathe underwater for a short time. They then have a conversation where Triton tells Percy about his own powers and how the ocean can be both a friend and a foe. This encounter plants the seed for Percy's future adventures in the underwater world.
It could be a dark wizard who has a vendetta against the Weasley family. Since Harry is with Bill and Charlie, he gets caught up in the conflict. This dark wizard might see Harry as an easy target because of his shyness, thinking he can be easily intimidated.
Well, in a 'sans meets bill cipher fanfiction', there could be some really interesting interactions. Sans, from Undertale, is known for his laid - back yet mysterious nature, while Bill Cipher from Gravity Falls is this chaotic and powerful entity. The fanfiction might explore how Sans would react to Bill's mind - games and manipulations. Maybe Sans would use his unique abilities like teleporting and bone attacks to counter Bill's tricks. It could also be a story of an unlikely alliance between the two, or perhaps a battle of wits and powers that keeps readers on the edge of their seats.
Yes, there are such fanfictions. Some authors like to explore the 'what if' scenarios where Harry's character takes a darker turn. It could be due to different upbringings in the fanfiction world, like being more influenced by the dark side of magic or having a different set of experiences that lead him to embrace darker magic from an early age.