Since we don't have much to go on, they could be anyone from adventurers to spies. Maybe they are characters who have been wronged in some way and form the alliance for revenge, or perhaps they are idealists aiming for a greater good but have to keep their actions secret.
Well, without more context, it's hard to say exactly. It might be a story that delves into the behind - the - scenes happenings of a secret alliance. For example, it could show how the members of the alliance met, what their initial goals were, and how they keep their alliance a secret from others. It could also involve some sort of conflict or challenge that they face as a secret group.
In Secret Alliance Fanfic, there could be a story where the alliance is made up of different species who have to overcome their differences to achieve a common goal. For example, a group of elves, dwarves and humans working together to save their land from a dark magic. They face many challenges like distrust among themselves at first, but as the story progresses, they learn to rely on each other's strengths.
One popular 'secret alliance fanfiction' story could be about two groups that secretly team up to fight a common enemy. For example, in a superhero fanfic, two rival superhero teams form a secret alliance when a new, more powerful villain emerges. They keep it a secret from the public to avoid chaos and use their combined powers to strategize and take on the bad guy.