One idea could be that Naruto accidentally uses the Reverse Harem Jutsu on himself instead of an opponent. He then has to deal with the chaos of multiple versions of himself with different personalities. For example, one might be super confident, another shy, and they all have to work together to solve a problem in the village.
A plot could involve the female characters in the Naruto universe being affected by the Reverse Harem Jutsu in a different way. Instead of being attracted to Naruto, they start to see all the male characters as part of a reverse harem. This could lead to some really funny and awkward situations as the characters' normal relationships are turned upside down.
Perhaps the Reverse Harem Jutsu gets out of control and spreads across the ninja world. Naruto has to go on a journey to find a way to reverse it. Along the way, he teams up with some unlikely allies, like some of the older and wiser ninja who have knowledge of ancient jutsu. They face many challenges, both from the effects of the jutsu and from those who might want to use the chaos for their own gain.
Well, perhaps a plot where the harem no jutsu is used not just for comical effect but to actually solve a complex political situation in the Naruto world. The various characters in the 'harem' could use their unique skills and influence to bring about peace. It could also be interesting to see how Naruto manages this new dynamic among the characters in his 'harem' and how it changes his relationships with them on a deeper level.
In fanfiction, the Naruto Reverse Harem Jutsu used on Kaguya could lead to some really interesting scenarios. Maybe it could be used as a comical moment to catch Kaguya off - guard. For example, she might be in the middle of some grand, menacing plan when suddenly the jutsu is cast and she's surrounded by a bunch of Naruto clones all vying for her attention in a rather silly way. This could potentially disrupt her concentration and give the protagonists an advantage in the fight.
The combination of two very different universes, Naruto and DxD, makes it interesting. The Reverse Harem Jutsu from Naruto is a fun element to introduce into the DxD world. It can lead to some really unique and unexpected interactions between the characters from both series.
Often, it can show a different side of Kaguya. She's so powerful and usually in control, but the jutsu can make her seem more vulnerable as she has to deal with this strange and unexpected situation. For example, she might have to waste time trying to figure out what's going on with these clones instead of focusing on her main goals.
In some fanfictions, the Harem Jutsu plotline involves Naruto accidentally using it on a group of powerful female ninja who then become obsessed with him. This leads to all sorts of chaos as Naruto tries to figure out how to reverse the effects while also dealing with the newfound attention. And there are also fanfictions where the Harem Jutsu is enhanced by some magical or mysterious force, making it even more powerful and unpredictable.
Here's a cool idea. In a 'Naruto Shadow Possession Jutsu Fanfiction', the jutsu could be passed down through generations in a family, but with a curse. Every time it's used, it slowly drains the user's life force. A young heir of this family has to find a way to break the curse while still using the jutsu to protect their loved ones. Another plot could be that an enemy uses the Shadow Possession Jutsu to create an army of shadow - controlled puppets. Naruto and his team must find a way to stop this without harming the people who are being controlled. And then there could be a story where the jutsu is combined with a new type of chakra, creating a whole new set of abilities that the main character has to master.
One idea could be a story where the main character uses Oriko Jutsu in a unique way to communicate with the Kyuubi. Maybe they form an unexpected alliance to face a new, powerful enemy in the Naruto universe.
One idea could be a story where Naruto discovers a new, ancient space - time jutsu that allows him to travel to alternate universes. In these universes, he meets different versions of his friends and enemies, and has to find a way to return home while also dealing with the chaos caused by the jutsu's power.
One interesting idea could be exploring new and unique ways the expansion jutsu can be used in battles. For example, using it not just for physical size increase but also for expanding the range of other jutsus.
Some fanfictions might explore the idea of combining Forbidden Jutsus. Picture a scenario where a rogue ninja combines a Forbidden Jutsu of destruction with a Forbidden Jutsu of mind control. This could create a super - powerful and extremely dangerous new ability, and the story could follow the efforts of the main characters to stop this new threat.