At first, Naruto would likely be very confused and hurt. He has always craved family love and acceptance, so this sudden turn would be a huge blow. He might try to plead with his family, asking them to believe him and give him a chance to explain.
His family would probably be overjoyed. After all, they might have thought they'd lost him forever. There would be hugs and tears, and a flood of questions about his life and what he's been through.
Shikamaru, being the laid - back yet perceptive friend, would probably think that Naruto has a plan. He would be concerned but also understand that Naruto is not one to make hasty decisions without a good reason. He might keep an eye on Naruto's family in his absence and hope that Naruto will return safely one day.
A simple Nezuko and Zenitsu fanfiction could be that they go on a journey together. Along the way, they encounter other demon slayers who are initially skeptical of Nezuko. But Zenitsu stands up for her, explaining that she's different. This shows the depth of their friendship and how Zenitsu has come to trust Nezuko completely.
One common theme is self - discovery. Since Zenitsu has a complex personality, many fanfics focus on him finding out more about himself, his powers, and his place in the world. Another theme is friendship. He often forms strong bonds with other characters in fanfics, like Tanjiro and Inosuke.