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.
Muzan was ultimately defeated by the collective efforts of Tanjiro, Nezuko, and the other demon slayers. Their teamwork and perseverance were key to ending Muzan's reign of terror in the manga.
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.
Well, muzan x reader fanfiction often explores a very interesting relationship. In such fanfictions, the writer usually dives deep into the dynamic between muzan, who is a complex and often dark character, and the reader - insert, which can be a very exciting exploration of power, mystery, and sometimes a touch of romance. It allows fans to put themselves in a fictional world with muzan and experience different scenarios.
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.
Transformation is another popular theme. It could be the reader - insert changing muzan, or the other way around. Maybe the reader - insert is transformed into a being like muzan, or muzan starts to change his ways due to the influence of the reader - insert. These themes add depth and intrigue to the muzan x reader fanfiction.
Well, identity is a common theme too. In 'female Muzan fanfic', the exploration of what it means to be Muzan as a female in a world that is mostly dominated by male demons. There's also the theme of survival. How does a female Muzan survive in a world full of threats? Some fanfics might show her using her wits and power to outsmart her enemies and stay on top.