He might be surprised at first. After all, having his tail back is a big change. He could start to explore the new sensations and abilities that come with it, like better balance perhaps.
In this fanfiction, Gohan's reaction could be complex. On one hand, it might remind him of his childhood when his tail was a part of him. He could feel a sense of nostalgia. On the other hand, he is now more in control of his powers. So he might initially be cautious, testing out what having the tail means in terms of his control over his Saiyan instincts. He may also worry about how others, like his family and friends, will react to his tail growing back.
Perhaps it was the result of a special training or a new form of energy absorption. Gohan might have been exposed to a new type of ki or energy that stimulated the regrowth of his tail. For example, if he was in a place with a high concentration of a certain type of energy that interacted with his Saiyan cells in a way that caused his tail to grow back.
One possibility is that it could be a genetic anomaly. Maybe something in his Saiyan genes that was dormant suddenly activated, causing the tail to grow back. In the Dragon Ball universe, Saiyan genetics are complex, and there could be some unexplored factors at play.
Well, in Dragon Ball lore, Gohan's tail was a Saiyan trait. In this fanfiction, it might mean he has more access to his Saiyan instincts. Maybe he can transform more easily into a Great Ape or use some of the primal Saiyan powers that were associated with the tail.
Gohan's powers could be a great addition to the Fairy Tail universe. His Saiyan strength and ability to go Super Saiyan would make him one of the most powerful mages in the guild. He could use his ki blasts like powerful magic attacks, and his speed and agility would be useful in battles against dark guilds.
Probably Natsu. They both have a strong sense of justice and are very powerful fighters. Natsu's fire - based attacks and Gohan's ki blasts could make for some amazing combined attacks in battle.
One scenario could be that Goku enters a special realm where time and space work differently. In this realm, the laws of biology are altered, and his tail simply regrows. Another might be that an enemy's attack, instead of harming him further, accidentally triggers a hidden regenerative ability in Goku that causes the tail to grow back.
In some fanfictions, it might grow back due to magical or alien forces. For example, a powerful wizard in the fanfic universe could use a spell to regrow it. Another way could be through some sort of advanced medical technology created by the Saiyans or their allies.
The tail - growing - back process might have a profound impact on Saiyan culture. In their society, the tail has always been a part of their physical identity. If it grows back, it could change the way they view their own strength. For example, they might develop new fighting styles that incorporate the use of the tail more effectively. And it could also influence their mating rituals as the tail is often associated with Saiyan's primal instincts.
Gohan will most likely encounter other Z - fighters like Krillin and Tien. They were all part of the group back then. Also, there's a good chance he'll meet Master Roshi. Roshi was a key figure in Goku's training, so his interaction with Gohan could be really interesting. He might also come across Bulma, who was always involved in the Dragon Ball story, either by accident or because he needs her help with some time - related technology or something.
One interesting aspect is the power combination. Gohan has his Saiyan powers like super strength, speed, and ki blasts, while Fairy Tail characters have their unique magics. When these two different power systems interact in fanfiction, it creates really cool battle and adventure scenarios. For example, seeing Gohan use his ki to enhance a Fairy Tail mage's spell or vice versa.