One idea could be a story where Logan, who is often seen as the antagonist in Fable 3, has a change of heart due to the influence of the princess. X could be a mysterious force or item that brings them together. For example, the princess discovers that Logan has been secretly trying to protect the kingdom from a greater threat that no one else is aware of, and X is the key to unlocking the truth about this threat.
For many fans, it's the chance to explore a different side of the characters. In fanfiction, the writer can take the basic traits of Logan and the princess and develop them in new and unexpected ways. For instance, the princess could be a strong - willed fighter in some stories, or Logan could show a softer side that we don't see in the original source material.
For Logan, you can start by giving him a backstory. Maybe he had a tough childhood that made him strong and resourceful. His actions in the fanfiction can then be influenced by this past. For the princess, show her growth from a sheltered royalty to a strong leader. She could learn from Logan's street - smart ways and he could learn about courtly manners from her.
X could play the role of a catalyst. For instance, if X is a magical amulet that Logan discovers. He initially wants to use it for his own gain but then realizes that it could be a powerful tool to help the princess save the kingdom. This realization makes him change his attitude towards the princess and they start to work together.
One idea could be that Logan, a commoner in the world of Fable 3, saves the princess from a dark magic spell. As he breaks the spell, they start to have a connection. He then accompanies her on a journey to restore peace to the kingdom which has been ravaged by the aftermath of the spell. Along the way, they face challenges that test their relationship and grow closer.
If Logan is a warrior and the princess is in need of protection, he could be assigned to guard her. At first, they might not get along well. The princess could find Logan too rough around the edges, and Logan might think the princess is too pampered. But as they face battles together, Logan sees the princess's courage and intelligence in strategic planning, and the princess sees Logan's loyalty and selfless acts of protection. This mutual admiration can lead to a deeper relationship.
One idea could be that Logan is a commoner who discovers he has a special power that is connected to the princess in Fable 3. They meet by chance when the princess is on a quest to find a solution to a dark magic that is plaguing the kingdom. Logan uses his power to save the princess from a dangerous creature, and from there, a bond begins to form between them as they work together to save the kingdom.
You can try fanfiction platforms like Archive of Our Own (AO3) or FanFiction.net. Just search for 'Logan x Princess' on their search bars, and you'll likely find relevant stories.
One idea could be a story where Logan helps Virgil and Roman understand each other better. Logan uses his logic to analyze their differences and find common ground for them. Maybe they are working on a project together in the mindscape and initially clash, but through Logan's mediation, they start to see the value in each other.
I really like 'Logan's Unspoken Love'. In this fanfic, the author does an amazing job of showing Logan's tough exterior but soft heart when it comes to the reader. It's full of little details that make the relationship seem so real. 'The Journey with Logan' is also good. It follows the reader and Logan as they travel across the country, facing various obstacles along the way. And 'Logan's Promise' is a touching story where Logan makes a promise to the reader that he will always protect them.