Yes, there might be such a fanfiction out there. Fanfiction often explores dark and alternative storylines. However, it can be quite a controversial and dark concept as Tony and Peter have a mentor - mentee relationship in the mainstream Marvel stories.
Maybe in the fanfiction's universe, the rules for obtaining the Soul Stone are different. It could be that the Stone demands a sacrifice of someone with a pure heart like Peter, and Tony, in his desperation to stop an even greater evil, makes the ultimate sacrifice. Another reason could be that Tony is being manipulated by some dark force. This force convinces him that killing Peter for the Soul Stone is the right thing to do, and Tony, believing he is doing the greater good, goes through with it.
One possible motive could be that the souk stone has some sort of power that Tony is desperate to obtain. Maybe it can grant him ultimate power or fulfill a long - held desire, and Peter is just an obstacle in his way.
In yaoi fanfiction involving Tony Stark and the Soul Stone, it could be a very creative exploration. Writers might imagine unique relationships where the power of the Soul Stone somehow intertwines with Tony's character. Maybe it creates a deep emotional bond between him and another character in a romantic or soul - connecting way that goes beyond the normal MCU storylines.
In a Peter Parker - Soul Stone fanfiction, the Soul Stone could give Peter new powers. For example, it could enhance his ability to sense danger even more, or it could allow him to communicate with the souls of those he has lost, like his Uncle Ben. This would add a whole new layer of depth to his character and his story.
In the original storylines, Tony and Peter often have a mentor - mentee relationship. So, in this fanfiction, the act of Tony killing Peter is a huge deviation. It goes against the bond they usually share.
A plot could involve Tony being the Soul Stone in a more metaphorical sense. For example, his intelligence and self - sacrifice are seen as the qualities of the Soul Stone. The story could show how his actions and decisions are like the power of the Soul Stone, influencing the fate of the other characters. He might sacrifice himself in a way that is similar to how the Soul Stone was used in the original story, but in a more emotional and character - driven way.
In fanfiction, Tony Stark may be linked to the Soul Stone in a way that it affects his character arc. The Soul Stone could represent a temptation for him. Given his complex personality, the power of the Soul Stone might either corrupt him or make him a better hero. It could also be that he is the only one who can resist the dark side of the Soul Stone's power, and this makes him a crucial figure in the fanfiction's plot related to the stone.
Peter could find the Soul Stone while on a school trip. He might be exploring an old museum or a historical site when he senses something strange. Following his instincts, he discovers the Soul Stone. This discovery would then lead to a series of events where he has to keep it hidden from his enemies, like the Green Goblin or Doctor Octopus.
In the fanfiction world, there could be a prophecy or a pre - determined fate that Tony believes in. He may think that Peter's sacrifice is necessary to fulfill this prophecy and save the world from some greater threat related to the Soyl Stone. He might see it as a selfless act in the long run, even though it seems cruel.