One idea could be that Naruto discovers the tanto in an ancient shinobi relic site. He initially doesn't know how to use it but with the help of Kakashi, he starts to learn. The tanto could have some special powers, like being able to cut through chakra - based defenses. This would add a new dimension to Naruto's fighting style.
Imagine if the tanto was a gift from a mysterious stranger. This stranger could be an ally or an enemy in disguise. Naruto would be suspicious but also intrigued. As he tries to figure out the stranger's motives, he also has to deal with the tanto's unique abilities. Maybe the tanto can transform into different shapes, and Naruto has to learn how to control this transformation in the heat of battle.
Sasuke could be her mentor. He has extensive knowledge of various weapons and his skills with bladed weapons are well - known. He could teach Naruko how to hold the tanto properly, the different stances for attack and defense, and how to use chakra with it for enhanced strikes.
One idea could be that Naruto catches a cold because he overexerted himself during the training trip and didn't take proper care afterwards. Maybe he pushed his body too hard with new jutsu training. His friends, like Sakura, could then take care of him, bringing him hot soup and medicine. It would be a sweet moment showing their friendship.
The unique weapon, the tanto. It adds a new element to the Naruto universe. It can be used in combat in ways different from the regular ninja tools we see in the original series.
A cool plot could be Naruto being reincarnated as an enemy of Konoha in a parallel universe. He has all his memories but has to fight against his former friends and home. This would lead to a lot of internal conflict for him. Also, he could be reincarnated into a time where there are new and strange forms of chakra that he has to learn to master in order to save the world again. For example, a chakra that is a combination of nature and spiritual energy.
One idea could be that Naruto gets tattoos as a form of self - expression in prison. Maybe he uses the tattoos to tell his story or to mark his growth. For example, he could get a tattoo of the Hidden Leaf symbol but with a twist, like it's broken in some way to represent his broken relationship with his village while in prison.
There's also 'Tanto Tales in Naruto'. This fanfic tells various short stories related to the tanto. It's great because it shows different perspectives of characters when it comes to the tanto, like how a young ninja discovers an old tanto and the adventures that follow.
One possible plot could be that Naruko discovers the tanto in an old family heirloom chest. She then starts to train with it secretly, knowing that in her world, having an unregistered weapon like this could get her in trouble. As she trains, she discovers unique abilities the tanto has, like being able to cut through certain magical barriers.
Perhaps the cause of Kagome becoming a child in the fanfiction could be a cursed spell from a powerful demon. This demon might have wanted to weaken Kagome's powers as she was a threat. As a child, Kagome could have some child - like innocence and different abilities. For example, she might be able to communicate with certain spirits more easily because children are often seen as more pure in such fictional settings.
The tattoo could also be a part of a deal she makes in the fanfiction. Suppose she has to make a pact with a powerful being in the feudal era. As a result, she gets a tattoo that binds her to the deal, and throughout the story, she has to figure out how to fulfill the terms of the pact without sacrificing her own values.