In fanfiction, the 'last time' could be a time of celebration. Maybe their guild had achieved a great victory and Erza and Mirajane were part of the celebration. Erza was probably still maintaining her serious demeanor but secretly enjoying the moment, while Mirajane was more openly jubilant, spreading the cheer among the guild members.
Well, in many fanfictions, 'last time' could refer to their last encounter in a battle. Maybe Erza and Mirajane had a fierce fight against a common enemy last time. Erza with her strong will and powerful sword skills, and Mirajane with her unique transformation magic. It could be that they had some differences in their battle strategies but still managed to achieve victory together.
One possible fanfiction could be about Naruto visiting the Fairy Tail world and teaming up with Erza and Mirajane. They could go on a quest together to defeat a powerful dark wizard. Naruto's unique ninja skills would blend well with Erza's swordsmanship and Mirajane's takeover magic.
They could start by meeting in a strange, in - between world. Naruto is intrigued by Erza's armor and Mirajane's different forms. They soon realize they have a common goal, which is to find a way back to their own worlds. As they journey, they share stories of their past adventures, with Naruto talking about his battles in the Hidden Leaf Village and Erza and Mirajane sharing tales from Fairy Tail.
One possible fanfiction could be about Naruto ending up in the Fairy Tail world and teaming up with Erza and Mirajane. They could go on adventures together, with Naruto's unique ninja skills complementing the magic of Erza and Mirajane. For example, Naruto's shadow clone jutsu could be used in creative ways during battles against powerful foes in the Fairy Tail universe.
One idea could be a crossover where Naruto, Erza, and Mirajane are brought together by a powerful magic spell that goes wrong. They have to work together to reverse the spell's effects while also dealing with the differences in their worlds. Naruto's ninja skills, Erza's swordsmanship and armor changing abilities, and Mirajane's demon form and magic could create really interesting interactions and battle scenes.
In a more complex fanfiction, Naruto, Erza, and Mirajane could be brought together by a prophecy. The prophecy states that only by combining the power of a ninja from Naruto's world and the mages from Fairy Tail can a great evil be defeated. At first, they struggle to understand each other's ways, but as they train together, they start to blend their skills. Naruto might teach them some stealth techniques, while Erza and Mirajane show him how to better utilize chakra - like energy in their magic. This would lead to some really epic battles against the evil force as they learn to fight as a team.
Growth is another theme. Writers like to show how Natsu, Erza and Mirajane develop their magic skills and as individuals over time. For example, Natsu might learn to control his power better, Erza becomes more strategic in battles, and Mirajane discovers new aspects of her magic.
The fact that fanfiction allows for creativity outside the bounds of the official story. Writers can put Mirajane and Erza in different settings, time periods, or even alternate universes. This gives a lot of room for unique plotlines. For example, they could be in a modern - day high school setting or a fantasy world different from their original one. The lemon aspect then comes into play to show a different side of their relationship, which can be both exciting and thought - provoking for readers.
Naruto might be curious about Erza's armors and Mirajane's demon form. He would probably ask a lot of questions. Erza would be impressed by Naruto's tenacity and his ability to never give up. Mirajane could bond with Naruto over their shared sense of protecting their friends. They could all train together, with Naruto showing his ninja training methods, and Erza and Mirajane teaching magic - based combat.