A really cool plot idea would be that Naruto is part of a prophecy where the one with bat wings will save the ninja world from a new, flying - based threat. His bat wings give him unique abilities in combat, like the ability to perform aerial acrobatics that no other ninja can. He has to train hard to master these new skills. His friends initially might be a bit shocked but then support him as he embarks on this new adventure to protect the world.
Perhaps Rouge is sent to the Naruto world to retrieve a powerful artifact that has been lost there. She enlists Naruto's help as he knows the land well. As they search for the artifact, they encounter many challenges like other ninja clans who also want the artifact. Naruto's ninja skills and Rouge's acrobatic and thieving abilities combine to make a great team.
One idea could be that Naruto discovers he has the power to manifest angel wings. This new power could make him an outcast at first, as it's so different from his normal ninja abilities. People might fear or envy him. But then he uses these wings to save the village in a unique way, like flying above to spot an approaching enemy army early.
Maybe the wings are related to a new form of chakra she discovers. As female Naruto experiments with different chakra natures, she accidentally unlocks this winged form. This form could have unique abilities like being able to fly at supersonic speeds or creating powerful wind-based attacks with the flaps of her wings. It could also lead to a storyline where other ninja clans become jealous or fearful of her new power and try to either steal it or get her to suppress it.
Perhaps the bat summon is from a cursed place, and when summoned, it brings a dark influence. The Naruto characters then have to find a way to break the curse on the bat and its place of origin. This could involve a journey to discover the history of the bat summon and the secrets of the place it comes from. It would be a story full of mystery and danger.
The wings could also play a role in Naruto's relationship with other characters. For instance, Hinata might be in awe of his new appearance with wings. This could strengthen their bond. Or, some of his friends could be jealous of his new power. Naruto would then have to deal with these emotions while also trying to use his wings for the greater good. He could use them to quickly transport medical supplies during a war or to rescue hostages from a far - off location.
The little bat could discover a hidden cave filled with ancient bat artifacts. It then has to protect this cave from other animals who might want to take over or destroy it. This could involve making alliances with other bats and using its wits to outsmart the invaders.
Perhaps the demon wings are a manifestation of a new form of chakra. In the fanfiction, Naruto could struggle to control this new power at first. As he learns to master it, he discovers that the wings not only give him physical advantages but also connect him to an ancient and powerful force within the ninja world. He might have to face off against enemies who are both envious and fearful of this new power.
One idea could be that the bat family encounters a supernatural force that gives them new powers. For example, they might come across a magical amulet that allows them to fly without their gadgets for a short time.
One plot idea could be Naruto using his wings to rescue the girls in his harem from various dangerous situations. For example, he might fly them to safety when their village is under attack. Another could be that the wings are a symbol of a new power he has gained, and the girls in the harem are drawn to him because of this unique power.
Maybe Naruto's bat wings are a gift from a mysterious being. This gives him an edge in his ninja missions. He might start exploring caves and other dark places that normal ninjas can't reach easily with his new ability to fly. His friends might be a bit jealous at first but then see how useful it can be for the team as a whole.