One common theme is redemption. Callisto has a dark past, and in many fanfictions, love from Xena helps her find redemption. For example, in some stories, Xena's love makes Callisto question her vengeful ways and strive to be a better person.
One great piece of Xena and Callisto love fanfiction is 'The Unlikely Bond' on FanFiction.net. It beautifully explores their complex relationship in a way that's both touching and true to their characters.
One possible reason is her acts of violence. Callisto was often on a warpath, attacking villages and people. So, her criminal actions could have led to her imprisonment.
One common theme is the journey of self - discovery. As they fall in love, both Xena and Gabrielle often learn more about themselves.
I'm not entirely sure which specific 'Xena Callisto in jail' story you're referring to. There could be different interpretations within the Xena universe. However, generally, Callisto was a complex character. If she was in jail, it might be related to her many acts of vengeance. Maybe she was captured after one of her raids or attacks against Xena or others. But without more context, it's hard to tell the full story.
One common theme is the protection of the baby. Since Xena and Ares are in a world full of danger, they have to constantly safeguard their child. Another theme is the change in their relationship. Having a baby forces them to reevaluate their feelings for each other.
One common theme is the exploration of their deep friendship. Fanfictions often focus on how they support each other through difficult times. For example, in many stories, Gabrielle helps Xena deal with her past traumas.
One common theme is adventure. Their romantic relationship is often intertwined with the dangerous quests they go on. Another theme is sacrifice. They are willing to sacrifice for each other, which is a big part of their relationship in fanfiction.
One common theme is friendship. Xena and Gabrielle's strong bond is often explored further in fanfics. For example, stories might show how their friendship endures through even tougher times than in the original series.
One common theme is physical injury. Usually, either Xena or Gabrielle gets hurt, like Xena getting wounded in a fight, and then the other one takes care of them. This shows their loyalty and love for each other.
Another theme could be magic and the supernatural. Neptune is often associated with the sea and has elements of the supernatural in many mythologies. Fanfictions might explore how Xena and Gabrielle interact with Neptune's magic or deal with magical creatures from Neptune's domain, which could lead to stories full of mystery and wonder.