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.
The guild master, Makarov, would be very protective. He'd see it as his duty to keep baby Erza safe. He might assign different members of the guild specific tasks like getting baby supplies or researching spells. Juvia would be over - the - top in her care for baby Erza. She'd constantly be fussing over her, making sure she's warm, clean and happy.
Honestly, 'y f n' in fanfic could be a random combination of letters without a widely recognized meaning. Maybe it's a made-up term by the author for a special plot element or character trait.
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.
I'm not entirely sure specifically what that particular 'bts y n is a hybrid hurt fanfiction' is about without more context. It could be a fan - created story that involves the BTS members, some kind of 'y n' (which might be a made - up or specific character in the fanfic world), and it's a 'hybrid' concept which could mean a mix of different elements like human and something else, perhaps supernatural, and 'hurt' might imply there are elements of pain or emotional distress in the story.
It can change the whole mood of the story. If Y N gets hurt, it might introduce a sense of urgency and concern into what was previously a happy and exciting concert - going experience.