Since we don't have more information about this fanfiction, it's difficult to determine the main character. However, if the theme of 'a thorn in my side' is related to something like guilt or a difficult decision, it might be a character like Asriel. He has a complex backstory with a lot of emotional baggage that could be considered a 'thorn in his side'. But again, this is just speculation.
Well, the Undertale story is centered around this idea of choice. You as the player enter a world beneath the surface where monsters live. The monsters have their own society and personalities. As you progress, you interact with them, and whether you decide to kill them or show mercy affects not only your immediate encounter but also the overall fate of the Underground and its inhabitants.
The integrity of Sans in fanfiction might also be reflected in his honesty. He doesn't deceive others easily. He may face difficult situations where lying could seem like an easy way out, but he chooses to be truthful. This aspect of his character makes him reliable and trustworthy in the fan - created stories.
One main theme is friendship. Just like in the game, many short stories focus on the relationships between the characters, such as the unlikely friendship between a human and a monster. Another theme is redemption. Some stories might show how a character who has made mistakes tries to make up for them.
I'm not entirely sure about all the main events as it's not clearly defined in a single official source. But it could start with a build - up of tensions between two groups, like the monsters and humans. Then there might be a major battle that sets the stage for the rest of the war.
Typically, characters like Frisk, a human who falls into the Underground, can be a main character in an 'Undertale Love Story'. Another could be Sans, the skeleton who is known for his unique personality. Papyrus, Sans' brother, might also be involved in some love stories as he has his own charm. And then there are other monsters like Toriel, who could potentially be part of a love - related plot as well.
Since it's a new story, it's hard to say for sure. But if it follows the original undertale's pattern, Frisk will likely still be a main character. Sans and Papyrus could also be important, as they are very popular characters in the undertale universe.
One main feature is the blend of characters. You often see Pokémon taking on traits of Undertale characters or vice versa. For example, a Pikachu might have the determination of Frisk from Undertale.
The main plot of Undertale full story involves a human falling into the Underground, a world of monsters. The human has to make choices throughout their journey, like whether to fight or show mercy to the monsters. These choices greatly impact the outcome of the story, leading to different endings such as the Pacifist ending where the human befriends all the monsters and helps them reach the surface, or the Genocide ending which is much darker and has a more tragic consequence for the Underground.
One main theme is choice. The player's choices throughout the game, like whether to fight or spare a monster, greatly impact the story. Another theme is friendship, especially seen in the pacifist route where the human forms bonds with the monsters.