Goku might become more in touch with his Saiyan heritage. His tail was a part of what made him a Saiyan originally, so getting it back could make him more aware of his roots. He could become more aggressive in battle, like how Saiyans are known to be.
Well, in a lot of fanfictions, the story might rewrite the rules of the Dragon Ball universe. So Goku could keep his tail simply because the author wants to explore different storylines with a tailed Goku. Maybe the author thinks it adds more to his character's appearance and abilities, like being able to use it as an extra limb in combat or for balance during his super - fast flying.
Another possibility is that a new form of training or power - up in the fanfiction is related to the tail. So Goku is made to keep it for his growth and development as a fighter.
If Goku never lost his tail, his powers and abilities might have developed differently. Maybe he would have retained some primal monkey-like traits that could have given him unique advantages or disadvantages in battles.
He could be a martial arts instructor. Goku is a master in combat, and teaching others his skills would be a great job for him. He could train students in the ways of martial arts, sharing his knowledge and experience.
For Goku's relationship with the other Z - Fighters, it could be a mixed bag. Some, like Piccolo, might see the tail as a potential weakness that enemies could target. So he might be constantly on Goku to protect it. On the other hand, Yamcha might be jealous that Goku has this unique feature that makes him stand out even more. However, overall, Goku's tail could also be a unifying factor. It could remind them all of Goku's alien origin and make them more aware of the vastness of the universe and the different species within it, which could strengthen their bond as a group.
Well, Goku's powers are extremely powerful. In Fairy Tail, magic is the main power source. Goku's ki-based abilities could be seen as a super-advanced form of magic. His super strength, speed, and energy blasts could make him a formidable ally or a terrifying foe. He could easily take on some of the stronger dark guilds by himself. Also, his ability to constantly grow stronger through training would be a unique aspect compared to the mages in Fairy Tail who mainly rely on learning new spells.
It could also be a symbol of a new power - up. In the Dragon Ball series, new physical changes often lead to increased power. So, getting his tail back might mean that Goku is about to reach a new level of strength. Maybe he'll be able to transform into a new form that is related to his Saiyan heritage and the presence of the tail. This could give him an edge in future battles against stronger opponents.
One interesting plot could be that Goku's tail gives him a new power. Since it's always been a unique part of him, perhaps it allows him to communicate with a certain race of creatures that are only attuned to the energy his tail emits. Another plot could be that he has to protect his tail from an enemy who wants to use it for some dark magic. The enemy believes that Goku's tail holds the key to unlocking a powerful spell, so Goku has to constantly be on guard while still going about his normal adventures.
Xu Fengnian was the one who pulled out the Demon Sealing Nails in Sword Snow Stride.
In chapter 422 of the novel, Xu Fengnian pulled out the Demon Sealing Nails from Xu Ying, Jiang Ni, Yu Youwei, Cui Hua, Sweet Potato, Pei Nanwei, Qing Niao, Xu Yanbing, Song Nianqing, Wu Liuding, Cui Hua, Luoyang, Sui Xiegu, Chai Qingshan, the first ancestor of Longhu Mountain, Zhao Xituan, the Jianghu people who died in the Yellow Yellow Formation of Sword Nine, and the armored soldiers who died in the Thirteen Armors of Spring and Autumn in the Longyao Prefecture of the Northern Mang to help them free themselves.
While waiting for the TV series, you can also click on the link below to read the classic original work of "Dafeng Nightwatchman"!