Erza is likely to be a main female character as well. She is strong and has her own unique relationship with Natsu. In this fanfiction, her reaction to Natsu leaving would be quite significant. She might be torn between her loyalty to the guild and her feelings for Natsu.
Lucy is usually one of the main female characters. She has a deep bond with Natsu through their adventures together.
Another main female character could be Wendy. She looks up to Natsu and would be greatly affected by his departure. Her kind and gentle nature would add an interesting dynamic to the story, especially in the context of the harem situation where she might be more reserved in expressing her feelings compared to the others.
It could be a group of rogue mages who have a vendetta against Natsu and Erza. They see the two leaving Fairy Tail as an opportunity to attack them when they are more vulnerable outside the protection of the guild.
Gray would be shocked at first. He and Natsu have a long - standing rivalry - but also a deep friendship. He might initially be angry that Natsu would just leave like that, but then he would realize how much he'll miss him. He might also feel a sense of loss for the guild as a whole, since Natsu is such an important part of it.
Lucy is definitely one of the most common. She has a close bond with Natsu from the start of the series. Erza is also often included. Her strong and confident personality makes her a great addition to the harem. Wendy could also be part of it. Despite her young age, she has a deep respect and admiration for Natsu.
In 'natsu leaves fairy tail harem fanfiction', a common storyline could be that Natsu leaves to seek his own power or identity outside of the guild and the harem. The female characters then form a sort of search party to find him. Along the way, they encounter different challenges that make them grow both as individuals and in their relationships with each other. This could also lead to some of them realizing that they don't just want Natsu back for the sake of the harem, but because they truly care about him as a person.
Gray could be one. Since he and Natsu have a long - standing rivalry, Gray might try to bring Natsu back to Fairy Tail. He'd be conflicted between his annoyance with Natsu and his concern for his former guildmate.
There could be a mysterious old wizard who takes Natsu under his wing when he leaves Fairy Tail. This wizard might have knowledge of ancient magics that Natsu is eager to learn.
Obviously, Natsu himself is a central character. He is the main attraction in the harem scenario. His fiery personality and powerful magic make him a key figure. Then there's Lucy. She is often included in the harem as she has a strong bond with Natsu in the original Fairy Tail series. Her celestial spirit magic also adds an interesting element to the fanfiction. Happy, the blue flying cat, is also popular. He can provide comic relief and also plays a role in the adventures, especially when it comes to helping the children in the story.
Seilah is also a main character in this context. She has her own set of powers and a rather complex personality in the Fairy Tail universe, which can be further explored in fanfiction.
Lucy could be a main character. She was always close to Natsu in the original Fairy Tail. So when Natsu returns as an 'ex' and meets the guild again, she would likely play a big role in how he is received and in the development of the story.
Gray would be one of the main characters to interact with Natsu. Their friendly rivalry is well - known in Fairy Tail. Makarov, as the guild master, would also have an important role in interacting with Natsu. He might give Natsu some important tasks or just have a grandfatherly chat with him about his return.