Perhaps there was a prophecy in both the Naruto and Fairy Tail universes that foretold of this male descendent. He could grow up in the Naruto world, but as he discovers his connection to Erza, he starts to learn about her world. He might develop a unique fighting style that incorporates Erza's armor - based combat and Naruto's chakra - based techniques. For instance, he could use his chakra to enhance the strength of Erza - like armors that he summons. This would make him a very interesting and powerful character in the fanfiction.
Well, one way it could work is through some sort of multiverse or time - travel concept. Maybe in a world where different anime universes collide. The Naruto male character could inherit some of Erza's traits like her determination and combat skills. He might also have a similar sense of justice. For example, if he has her magic in some form, he could use it in a way that combines with his ninja abilities, like using her requip magic to quickly change weapons during a fight, similar to how a ninja would use different tools.
His abilities would be a blend of the two worlds. He could have Erza's ability to sense magic and Naruto's ability to sense chakra. This would give him an edge in detecting enemies. He might be able to create clones that are part ninja clone and part magical projection, like a combination of Naruto's shadow clones and Erza's magic. His physical strength could be enhanced by both Erza's training in the Fairy Tail guild and Naruto's training as a ninja. He could also have the ability to teleport short distances, a combination of Naruto's body flicker technique and Erza's magic - based movement abilities.
Erza Scarlet's tattoos can be incorporated into a Naruto fanfiction in diverse ways. Maybe the tattoos are a result of an experiment by Orochimaru - like figure in the Naruto world, trying to combine different forms of power. They could also be a form of spiritual connection to a new type of summon in Naruto, say a powerful beast that only responds to those with such tattoos. Additionally, her tattoos could be a map or a code in the Naruto world that leads to a great treasure or a secret place filled with powerful ninja techniques.
It could start with Naruto being found in the Fairy Tail world as a baby, with Erza taking him in as her own. She might notice something special about him right away, like his strong will that reminds her of herself. Then as he grows up, he starts to show signs of both ninja and magic abilities, which puzzles everyone in the guild but also makes them excited to see what he'll become.
Well, in this fanfiction concept, it could work in terms of Naruto's protective nature. Naruto is known for his loyalty and his will to protect those he cares about. If he were Erza's older brother, he would surely use his skills and abilities to keep her safe. He could teach her some of his ninja techniques, which would be really cool to see combined with Erza's own combat skills. Also, Naruto's positive attitude could influence Erza in a different way, making her more open and perhaps less brooding at times.
Well, the plot could involve Naruto growing up in the Fairy Tail world with Erza as his mother. He might inherit some of Erza's strong - willed and determined nature, as well as Naruto's own unique ninja abilities. Maybe he has to face some sort of threat that combines elements from both the Naruto and Fairy Tail universes.
Well, Naruto leading bandits could be an interesting twist. Maybe he's been brainwashed somehow. He could use his ninja skills to lead them in a different way than typical bandits. For example, instead of stealing for greed, they could be stealing from the rich to give to the poor, like a ninja Robin Hood situation.
Well, one way it could work is if Naruto somehow enters the Dragon Ball universe. Naruto's skills like his shadow clones could be interestingly pitted against Frieza's power. Maybe Naruto would be initially in awe of Frieza's strength but then find ways to outwit him using his ninja tactics.
Well, one way it could work is by exploring Naruto's sense of justice in the context of Lucifer's world. Naruto is all about friendship and protecting the village, while Lucifer has his own complex view on good and evil. Maybe Naruto could be transported to Lucifer's realm and try to bring his values there, causing a clash or an interesting fusion of ideologies.
Well, one way it could work is if Naruto's world somehow got merged with the dark and chaotic world of the Joker. Maybe Naruto, after facing so much pain and loss in his own world, starts to adopt the Joker's nihilistic views. He could use his ninja skills in a more unhinged way, like the Joker uses his chaos-creating abilities.
Well, the plot could revolve around Erza instilling discipline in Naruto. Naruto is often impulsive, and Erza, with her strict military - like upbringing in the Fairy Tail guild, could help him become more focused. For example, she could make him train in a more methodical way, similar to how she trained in swordsmanship.