Goku would probably get along well with Natsu. They both have a love for fighting and a strong sense of justice. They might constantly challenge each other to friendly battles to see who's stronger.
When it comes to Erza, Goku would respect her leadership and fighting skills. Erza, in turn, would be intrigued by Goku's different power source and his ability to constantly grow stronger. They could have some intense training sessions together, with Goku learning about Erza's different armors and combat techniques, and Erza learning about Goku's Super Saiyan forms and ki control. His presence would also add a new dynamic to the Fairy Tail guild, as his carefree and adventurous personality would mix with the diverse personalities of the existing members.
With Lucy, Goku would be a bit of an enigma at first. But as time goes on, she would likely be amazed by his power and his simple - minded yet noble nature. He might protect her during battles in a very straightforward way, just like he does with his friends on Earth. And Goku would be interested in the Celestial Spirits that Lucy can summon, seeing them as unique allies.
Well, Goku's powers are mainly based on ki manipulation, which is somewhat similar to magic in the Fairy Tail world. If he joins Fairy Tail, he could probably learn to combine his ki with the magic of Fairy Tail. For example, he might be able to infuse his ki into Natsu's fire magic to make it even more powerful. Also, his teleportation technique, like Instant Transmission, could be a great asset during battles and rescue missions in the Fairy Tail universe.
One aspect that could be explored in this fanfiction is Gajeel's growth in magic. As a kid joining Fairy Tail, he would be exposed to different types of magic and training methods. Maybe he starts off with his Iron Dragon Slayer magic being quite basic, and then with the help of the guild's masters and other members, he refines it. He could also learn new skills that complement his existing magic, which would not only make him stronger but also show his development within the guild.
Well, in such a fanfiction, Gajeel would bring a whole new energy. He might be more rebellious as a youngster. His journey to find his place in Fairy Tail could involve getting into small scuffles with other members at first. But as time passes, he realizes that Fairy Tail is a place where he can belong. His growth could be shown through his changing attitude towards the guild's rules and values.
If Kakashi were to join Fairy Tail, it would be an interesting mix. Kakashi is a highly skilled ninja from the Naruto universe, known for his Sharingan and diverse jutsu. In Fairy Tail, he'd likely bring in a whole new set of combat techniques. His calm and collected demeanor would contrast with some of the more boisterous members of Fairy Tail. He might also form interesting relationships. For example, he could bond with Erza over their shared combat experience and sense of justice. And his intelligence could be used to help plan strategies for the guild's battles.
Imagine Goku meeting Lucy. Lucy, being a celestial spirit mage, would be fascinated by Goku's power. Goku, on the other hand, might not understand the concept of celestial spirits at first. But as they interact more, Goku could help Lucy become stronger physically, while Lucy could introduce Goku to the magical side of the Fairy Tail world. Goku could also have interactions with Gray. Gray's ice - make magic would be a contrast to Goku's heat - based ki attacks. They could have friendly battles to test each other's strength.
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.
Their marriage could also lead to more diplomatic relations within the guild. Levy is friendly with most members, and Gajeel has his own group of comrades. Their union could bridge any gaps between different cliques in the guild. For instance, if there were disputes between the more bookish members and the combat - focused ones, Gajeel and Levy could step in and mediate, using their combined influence.
Well, one possible plot could be that Goku somehow ends up in the Fairy Tail world. He might initially be confused by the magic there, but then start to learn about it. He could team up with Natsu and the gang to fight against a powerful dark wizard. Goku's strength and his unique fighting skills like the Kamehameha could be a great asset to Fairy Tail in battles.
Kakashi's ability to manipulate chakra could be seen as a form of magic in the Fairy Tail world. His Sharingan could potentially unlock new forms of magic or enhance existing ones. For example, if he were to team up with Erza, his Sharingan could help her analyze her opponents' defenses better, allowing her to break through them more easily. His teleportation techniques could also be used to quickly move around the battlefield, something that would be very useful in large - scale battles against powerful dark guilds.
To write their character dynamics well, focus on their differences. Macao is a more experienced, father - like figure in the guild. Cana, on the other hand, is a bit more carefree. Have Macao be the voice of reason when Cana gets into some of her more impulsive ideas. For example, when Cana wants to take on a dangerous mission alone, Macao could step in and say they should plan better.