Well, in this type of fanfiction, a recurring theme could be the struggle between good and evil. Loki has his own morally ambiguous nature, Tony is usually seen as a hero, and the demon represents the 'evil' or at least the otherworldly and potentially dangerous element. How these three elements interact and whether good can prevail over evil or if the lines between them blur is a common exploration in such fanfictions. Also, there might be a theme of discovery, as the characters discover new aspects of themselves and each other in this strange situation.
I'm not really into that specific type of fanfiction, but you can try searching on fanfiction websites like Archive of Our Own. They usually have a wide variety of fanfics, and you might be able to find some related to Loki, Tony, and demons there.
In fanfiction, Loki and Tony's friendship can be really interesting. They are both complex characters. Loki, with his mischievous nature, and Tony, the brilliant inventor. Their friendship might start from a mutual understanding of being different from the norm. Maybe Loki sees Tony's genius as something worthy of his respect, and Tony might be intrigued by Loki's otherworldly powers.
Natasha Romanoff would be an interesting character to include. She's very perceptive and could be the one to first notice the change in Loki's behavior towards Tony. And then there's Bruce Banner. His scientific mind could interact with both Loki's magic and Tony's technology, and he could also offer some unique perspectives on their relationship, perhaps warning Tony about the risks of getting involved with Loki.
Another reason could be the creativity of the fanfiction community. There are so many different interpretations and ideas in fanfiction. Tony and Loki, being characters with a lot of potential for different stories, would enjoy seeing all the creative ways fans reimagine them and their worlds.
One great Thor Loki Tony fanfiction is 'The Triumvirate'. It weaves an interesting story where their different powers and personalities collide and cooperate in a unique way. The author does an excellent job of capturing the essence of each character.
Yes, there might be some fanfiction out there with such a plot. Fanfiction platforms often host a wide variety of creative and sometimes out - of - the - box ideas. You can try searching on popular fanfiction websites like Archive of Our Own.
Their shared intelligence. Tony is a scientific genius and Loki is highly intelligent in his own way, especially in matters of magic and strategy. This can lead to some great moments where they outwit their opponents together.
The theme of acceptance is also prevalent. They come from different worlds, literally. Asgard and Earth have very different cultures and values. But as soulmates, they have to accept each other's differences. This can be seen in how they interact with each other's friends and families in the fanfictions. For instance, Tony introducing Loki to the Avengers and Loki introducing Tony to his Asgardian allies.