One adventure could be that they enter a mysterious dimension where Naruto's chakra is all messed up. Adult Naruto has to rely on his knowledge and kid Naruto has to rely on his pure and untainted chakra. Together, they figure out how to get out of the dimension and in the process, they learn more about the true nature of chakra and their own connection to it. It would be filled with lots of action, discovery, and some brotherly - like bonding between the two Narutos.
Maybe they'd embark on a mission to stop a new threat that's related to Naruto's past. Kid Naruto would be all excited and ready to fight, while adult Naruto would use his wisdom and more powerful skills to lead the way. They could also meet some of Naruto's old friends as kids and have some really fun interactions.
Well, in a fanfic where adult Naruto meets kid Naruto, it could be really interesting. Adult Naruto might be super proud of his younger self. He could give kid Naruto some tips on how to train better and how to deal with the loneliness he sometimes feels. Maybe he'd also tell him some spoilers about future events in a fun, teasing way.
They could go on an adventure to find a powerful treasure that combines the power of the One Piece and some kind of ninja - related artifact. Maybe they'd have to fight against a new enemy that is a combination of pirates and rogue ninjas. They might travel to new islands where Naruto's ninjutsu would be useful for exploring hidden caves, and Luffy's stretching ability would help them reach high places or cross large gaps.
They could go on adventures to discover ancient ninja secrets. Since they are the same age, they might team up to explore hidden places that are said to hold great power or knowledge. Maybe they would search for lost jutsu together and face various challenges along the way.
Maybe they embark on an adventure to help a small, oppressed village. They use their combined skills to overthrow the tyrant ruling the village and then stay for a while to help rebuild it. During this time, they learn about different ways of life and make new friends. This adventure would strengthen their bond and also their reputations as great shinobi.
Well, they could embark on a journey to find other tailed beasts and try to form a new kind of bond among them. This would be an adventure full of challenges as some of the tailed beasts might be hostile at first. Naruto and Kyuubi, as brothers, would use their combined strength and Naruto's persuasion skills to make peace with them. Along the way, they would also learn more about each other's capabilities and grow closer as brothers.
Well, for starters, they could embark on an adventure to protect the Sohma family from outside threats. Naruto, with his Rasengan and other jutsu, would be a formidable protector. They might also travel to hidden ninja villages together, with Tohru learning about Naruto's world. Or perhaps they go on a quest to uncover the secrets of Tohru's mother, and along the way, they encounter all kinds of challenges, like dangerous yokai or other ninja clans who are interested in the Sohma family's unique situation.
They could go on a quest to find a powerful magical artifact. Naruto's combat skills and Lucy's knowledge of magic could be useful in navigating dangerous dungeons and fighting off enemies who also want the artifact.
They could have adventures where they combine their skills. Naruto could use his ninja techniques like shadow clones, and Erza could use her different armors and magic. For example, they might fight against a powerful enemy that is a threat to both their worlds. Naruto's clones could distract the enemy while Erza changes into her strongest armor to deliver a powerful blow.
He could have adventures in search of rare ingredients. Naruto, with his ninja skills, would be great at traversing difficult terrains to find ingredients that Toriko wants. They might go to places like the Gourmet World, where Naruto would face new and strange creatures.
They could have a mission - based adventure. Maybe they are sent to a far - off land to retrieve a powerful and mysterious scroll. Naruto's determination, Neji's strategic thinking, and Tenten's weapon skills would make them a formidable team during the journey, facing various enemies and traps along the way.