He could summon a giant phoenix. In many fanfictions, a phoenix is a symbol of rebirth and great power. It would be an amazing addition to Naruto's arsenal. The phoenix could have the ability to heal Naruto and his allies in the heat of battle and also unleash powerful fire attacks on their enemies.
Naruto might summon a tribe of forest spirits. These spirits could be small and nimble, able to move quickly through the trees and gather intelligence. They could also use the power of the forest to create barriers and traps for Naruto's enemies. Since Naruto has a connection with nature through his own chakra, it would make sense for him to be able to summon these forest - loving spirits.
There's a chance he could summon a race of shadow warriors. These warriors are from a dimension of darkness and are experts in stealth and assassination. They would be a contrast to Naruto's usual bright and open - fighting style. But with proper training and understanding, Naruto could use them to take on enemies from the shadows, adding a new dimension to his combat capabilities.
One possible plot could be that Naruto discovers an ancient and forgotten summoning contract. He decides to make it his own, not knowing what kind of creatures it will summon. As he signs the contract, he is immediately transported to a strange and mysterious realm. There, he meets the initial summon, which is a powerful and intelligent being. This being tests Naruto's worthiness and eventually agrees to help him in his battles against new and dangerous foes in the Ninja world. This new summoning gives Naruto an edge in combat and also helps him gain more knowledge about the hidden secrets of the Ninja world.
He could summon different types of wolves. There might be large, alpha - like wolves that are very powerful in combat. Or perhaps smaller, more agile wolves that are great for scouting. There could also be wolves with special abilities, like ones that can control ice or fire, which would add a whole new dimension to Naruto's fighting style.
Sure. There could be a fanfiction with such a plot. Naruto is known for his ability to form unique bonds. If he were to sign a lion summoning contract, it would be interesting. The lions could have their own personalities and abilities. For example, they might be able to use fire - based attacks or have super - speed, which would add a new dimension to Naruto's fighting style.
It could be Kakashi too. Kakashi is very experienced and observant. He might notice Naruto's confusion or struggle with the new contract and offer his insights. He could share some of his own experiences with summons to help Naruto figure things out.
One of the most interesting demons could be a shape - shifting demon. This demon could change its form to deceive enemies or help Naruto in stealth missions. For example, it could transform into an exact replica of an enemy ninja to gather information. Another interesting demon might be a demon with the power of time manipulation. Naruto could use this demon's power to go back in time and prevent certain disasters from happening in the ninja world, like the attack on the Hidden Leaf Village by Pain.
Naruto himself could be the main character. Given his adventurous and selfless nature, he might be the one to make the contract to save his friends or the whole Hidden Leaf Village. He would then have to deal with the consequences and powers that come with the contract.
A great fanfiction concept could be centered around a group of rogue ninjas who steal the snake summoning contract. They use the summoned snakes for their evil deeds, causing chaos in the ninja world. A young, inexperienced ninja team is then tasked with retrieving the contract. Along the way, they learn about the history and power of the snake summonings, and they also face moral dilemmas when they realize some of the snakes are not as evil as they seem.
It could be a new, young ninja who stumbles upon the cobra summoning contract by accident. This would be an interesting take as they start from scratch learning about the cobras and their powers.
It could be a giant eagle - like creature. Eagles are often associated with freedom and power in many mythologies. Naruto could summon it to gain an aerial advantage in battles, allowing him to quickly move across the battlefield or scout areas from above.
It could be a side character from the original Naruto series who wasn't given much spotlight before. They find the hellhound summoning contract and it changes their role in the story completely. For example, a previously weak or overlooked ninja suddenly becomes a force to be reckoned with thanks to the hellhounds.