You can also start by introducing a new character who challenges their relationship. Maybe a new girl has a crush on Billy and Mandy gets jealous. In the heat of an argument to claim Billy as her friend (or more), she kisses him. This would create an interesting starting point for the fanfiction.
First, you should think about the relationship between Billy, Mandy and Brains. Decide if you want to focus on their friendship, rivalry or something else. For example, you could start with a situation like Billy accidentally breaking one of Brains' inventions that was important to Mandy.
Perhaps in a fanfiction where there's an alternate universe. In this universe, Billy and Mandy are normal kids without all the spooky stuff around them. They participate in a school play where they have to kiss as part of the script, and this kiss makes them see each other in a different light, starting a romantic sub - plot in this otherwise normal world for them.
Well, obviously Billy and Mandy are the main characters. Billy is often the goofy and naive one, while Mandy is more cynical and in control.
A possible plot is that the kiss was part of a bet. Billy lost a bet to Grim and as a result had to kiss Mandy. But then, unexpectedly, Mandy didn't mind as much as she thought she would and it led to a series of comical and heart - warming events in their little group.
First, think about the setting. It could be something like their home in Mewni or Echo Creek. Then, consider the emotions they are feeling. Are they nervous? Excited? Once you have these basics, you can start with a simple opening like 'Star and Marco stood in the garden, the air thick with anticipation.'
It's quite good. The comic has interesting plots and unique characters that make it enjoyable.
You can try some popular fanfiction websites like FanFiction.net or Archive of Our Own. They usually have a large collection of different fanfictions, including billy x mandy ones.
Begin with creating a mood. If you want a romantic and somewhat tense mood, describe the scenery in a way that reflects that. For instance, if it's a stormy night on the island. Then, introduce the characters' emotions towards each other. Gwen might be secretly attracted to Duncan but trying to hide it. Duncan, on the other hand, could be more forward in his interest. Develop their relationship through dialogues and small interactions until it reaches the climax of the kiss.
First, you can start by creating a detailed setting. Decide where Eddie and Patricia are when they kiss. Is it at school, in a park, or somewhere else? Then, think about their emotions leading up to the kiss. Are they nervous, excited, or something else? For example, if you want to create tension, you can write that Patricia has been secretly in love with Eddie for a long time and Eddie is completely oblivious until the moment of the kiss.
You can start by writing a short prologue about their relationship up to that point. What kind of adventures have they had together? How have their feelings for each other been evolving? Then, introduce the event that will trigger the kiss. It could be a revelation about one of their pasts that makes the other see them in a new light and leads to the kiss.