The main conflict might be the unrequited love. If the narrator loves a character deeply but Katara doesn't feel the same way, it could lead to a lot of emotional turmoil. The narrator may struggle with jealousy if Katara shows affection towards someone else. There could also be a conflict where the narrator tries to prove their love is greater, but Katara is either oblivious or not interested.
It could end with the narrator finally accepting that Katara will never love 'her' in the same way and moving on. Maybe they find someone else who appreciates their love.
Another possibility is that they are set in a modern - day fictional world with a bit of a magical twist. Sokka could be a popular guy at school or in a small town, the girl could be an artist or a musician, and the narrator is the shy, but deeply in - love outsider who feels Sokka doesn't truly understand the girl's soul like he does.
Perhaps the fanfic could explore the different ways the two characters show their love. Sokka might show his love in a more practical or protective way, while the narrator has a more emotional and passionate love. This contrast could lead to conflicts and misunderstandings between them.
The main characters could be Sakura and the narrator. But there might also be a new love interest for the narrator. This new person could be a complete opposite of Sakura. For instance, Sakura could be very outgoing and the new love interest could be more introverted. This contrast might play a role in the narrator's change of feelings towards Sakura.
One possible plot could be that the narrator has grown apart from Sakura over time. Maybe they had different life goals. For example, Sakura was too focused on her career and the narrator felt neglected. So, the narrator gradually lost the love they once had.
It could be that the character has found someone else who shows more care and attention. In fanfics, new characters can be introduced who are more in tune with the main character's emotional needs. Unlike Vegeta, who may be seen as too cold or unresponsive.
Another plot could be that the character who says this has met someone else who shows them a different kind of love and attention. They start comparing this new person to Vegeta and realize that they are no longer in love with Vegeta. This new relationship makes them see all the flaws in their relationship with Vegeta that they were previously overlooking.
One possible plot could be that Katara discovers she's pregnant in a time of relative peace in her world. She then has to deal with the reactions of her friends and family, like how Aang would respond as her partner. There could be challenges she faces during the pregnancy, such as dealing with her own fears and the expectations of her tribe.
Maybe in the fanfic, they are dancing to celebrate a victory over the Fire Nation. Aang has just defeated a powerful Firebender and Katara is overjoyed. They start dancing spontaneously, and their movements are a mix of Aang's Airbending - like grace and Katara's fluid Waterbending - inspired steps. They twirl and spin, and the onlookers can see the bond between them growing stronger.
Well, this kind of fanfic might explore a complex emotional shift. Maybe the author wants to show a new direction in the relationship between the characters. It could be due to some big changes in Vegeta's behavior or actions that led to this statement of no longer loving him.