Another plot could involve a crossover with the Harry Potter world. Erza could be a transfer student to Hogwarts. Her magic, which is different from the wizarding magic, would create a stir. She might have to face off against Voldemort's forces while also learning about the magical world of wands and spells.
One idea could be an Erza Scarlet crossover with the world of Harry Potter. Erza could be a visiting wizard from another magical realm. She might attend Hogwarts for a while, and her combat skills could be put to use in the Triwizard Tournament, adding a new and exciting dynamic to the traditional challenges.
One idea could be a story where they accidentally swap bodies. This would lead to a lot of comical situations as they try to adapt to each other's lives. They'd have to deal with different relationships within their respective guilds or groups while also learning more about each other's personalities.
One plot idea could be that a group of dark mages kidnap Erza to use her as a bargaining chip against her guild. They know her strength and reputation, so they think they can force Fairy Tail to give up some valuable magical artifacts. Another could be that an obsessed fan of Erza's kidnaps her, believing that she can be 'tamed' and made to love him. This could lead to a story of Erza having to outwit this deranged individual while also trying to escape from his clutches.
One idea could be exploring how Erza balances her pregnancy with her duties as a strong mage. Maybe she has to take a break from dangerous missions and feels a bit restless. Another could be the reactions of her friends in Fairy Tail. They might be overly protective or excited for her.
A cool plot could be that there's a magical artifact that has the power to grant any wish. Ichigo and Erza both hear about it independently and end up chasing it. When they meet, they initially think the other is an enemy. But as they start to understand each other's motives, they decide to share the wish if they get the artifact. However, they face many challenges along the way, like traps set by other people who also want the artifact. Erza's strategic mind and Ichigo's determination would be great assets in this adventure.
One popular idea is an Erza crossover with the Harry Potter universe. Imagine Erza attending Hogwarts and using her combat skills in magical duels. Another is a crossover with the Avatar: The Last Airbender world. Erza could learn bending techniques and fight alongside the Avatar. A third could be a crossover with the Naruto universe, where she might interact with ninja and use her magic in the shinobi world.
Goku from Dragon Ball Z. Goku's Saiyan power and his love for fighting strong opponents would mesh well with Erza. They could have a friendly sparring match at first, and then team up to face a greater threat, perhaps a powerful villain that endangers both their universes.
One idea could be that they discover the pregnancy during a mission. Maybe they are in the middle of fighting some powerful enemy when Erza suddenly feels unwell and realizes she might be pregnant. It could add a whole new layer of drama to the story, with Gray being overly protective.
Perhaps they could go on a journey to find a safe place for their child to be born. Along the way, they discover new things about each other and their relationship deepens. They might encounter different magical creatures or places that test their resolve and love for each other.
One idea could be exploring how their guild mates react to the news. Some might be overjoyed and offer all kinds of support, while others could be a bit shocked at first. Another could be focusing on how Natsu and Erza themselves adjust to the idea of becoming parents. Natsu might be a bit clumsy at first but full of enthusiasm, and Erza could be more practical and start planning everything right away.