Naruto would become more confident. Gojo's power is extremely strong, and having it would make Naruto feel like he could handle almost any situation. He'd also become more strategic as Gojo's power requires a different approach to combat compared to his normal ninja skills.
A possible plot is that with Gojo's power, Naruto is able to see the world in a new way. He can now perceive curses in the ninja world that were previously hidden. This leads to a whole new side - quest where he has to deal with these curses while still maintaining his duties as a ninja. He might also use Gojo's power to teach other ninjas a new way of fighting, changing the ninja combat system.
In Naruto fanfiction, one common power - up is related to new jutsu creation. For example, some fanfictions might have Naruto develop a jutsu that combines the power of all five chakra natures in a completely unique way. This could give him an edge over his enemies like never before. Another aspect could be the enhancement of his Sage Mode. Maybe he finds a way to make it more stable and powerful, allowing him to stay in the mode for a much longer time without any negative side effects. There are also fanfictions where Naruto gains the ability to control time, which is a completely new and overpowered concept that makes for really interesting stories.
Well, Gojo could be a super powerful outsider. Maybe he comes to the Naruto world to study its unique chakra system. His Infinity ability would be a game - changer. He could use it to easily deflect most ninjutsu attacks. And his Six Eyes could help him detect hidden enemies or traps that normal shinobi might miss.
In certain fanfic concepts, Naruto could get the phoenix power during a near - death experience. His strong will to survive and protect his friends could attract the phoenix spirit. The phoenix, known for its rebirth and powerful abilities, might choose Naruto as its host, seeing his indomitable spirit as a worthy vessel for its power.
Well, it could be that Naruto's strong will and his connection to all the other tailed beasts play a role. Since he has befriended the other tailed beasts, their combined energy or some sort of spiritual link might attract the power of the Juubi. For example, in some fanfic concepts, the tailed beasts' collective consciousness decides to merge their powers with Naruto, which includes the Juubi's power as the ultimate form of chakra.
In a fanfiction, Naruto having the power of the sun could potentially have a huge impact on the chakra system. Since the sun is such a powerful energy source, it might disrupt or enhance the existing chakra flow. He could develop new jutsu that are based on solar energy rather than just the normal chakra types. This could lead to a whole new set of skills and abilities that are unique to him, and it would force his opponents to completely re - evaluate their strategies when facing him.
He could have a 'Solar Sage Mode'. In this form, his body would be surrounded by a bright, sun - like aura. His physical abilities such as strength, speed, and agility would be enhanced to an extreme level. His attacks would also carry the power of the sun, like solar - powered punches or kicks that could cause massive damage.
He could play the role of a disruptor. Just like his character in his own universe, he would disrupt the existing power dynamics in Naruto. His overpowered abilities would make him a force to be reckoned with, whether he's on the side of good or bad.
One challenge could be controlling the new power. Just like Naruto had to learn to control the Nine - Tails' chakra, he'd have to figure out how to use Achilles' power without overexerting himself. Another might be dealing with enemies who would target his new weakness, if he has one like Achilles' heel.