Well, in this fanfic, Naruto's use of the Speed Force could lead to some really interesting crossovers. Imagine him meeting characters from the DC Universe who are also associated with the Speed Force. He could learn new techniques from them or teach them some of his ninja skills. In terms of the Naruto world, his newfound speed could make him a more elusive target. He could use it to quickly gather intelligence across different villages without being detected, completely changing the power dynamics in the world of ninjas.
His power level would skyrocket. The Speed Force gives him the ability to move at incredible speeds, which adds a whole new dimension to his combat capabilities. He can now dodge attacks with ease and also deliver rapid - fire strikes.
Naruto might develop a 'Force - Shadow Clone Jutsu'. He could use the Force to create shadow clones that are more durable and have some Force - related abilities. For example, they could use the Force to sense enemies or even share knowledge between each other more effectively.
The Akatsuki could still be the main antagonists. Even with Naruto having the power of the Speed Force, they would pose a significant threat. Their various unique abilities and their goal of collecting the tailed beasts would still be in conflict with Naruto's desire to protect the villages.
One interesting concept could be Naruto being able to access the Speed Force to quickly move between the Hidden Villages. This would give him an edge in battles and also in delivering important messages.
If Naruto were blessed by the speed force in a fanfic, it would completely change his fighting style. He could quickly close the gap between him and his foes, and his rasengan would be delivered in a blink of an eye. Also, his ability to gather information on the battlefield would be enhanced as he could zip around to different locations rapidly.
There are so many Naruto fanfics out there. For the 'godlike naruto uses a katana fanfic', you could also ask in Naruto - related fan communities. Reddit has some great Naruto sub -reddits where fans discuss and share fanfics. Maybe someone there has read or even written such a fanfic and can point you in the right direction.
One antagonist could be a corrupted version of one of Naruto's old friends. Maybe they were influenced by some dark force and now have powers that rival Naruto's. They would oppose Naruto not only because of the power of the kyoketsu shoge but also due to their twisted view of the ninja world. Also, there could be a group of interdimensional invaders who see Naruto's power and the kyoketsu shoge as a threat to their plans of conquering the ninja world. They would use their advanced technology and unique abilities to try and defeat Naruto.
The plot could involve Naruto being in a super - powerful form (godlike) and using the kyoketsu shoge in unique ways. Maybe he uses it to fight against powerful new enemies that are immune to his regular jutsu. He could also use it to protect his village in a more stealthy and unexpected manner compared to his usual flashy attacks.
It would probably be about Naruto having some sort of god - like abilities. He would use a katana in combat, perhaps with skills far beyond what he has in the original series. For example, he could use his godlike chakra to enhance the katana's strikes or even use it to perform special jutsu that are unique to this fanfic concept.