Yes, it can be quite popular. Many Naruto fans are intrigued by the idea of Naruto having such an extraordinary lineage as being the son of Kaguya Otsutsuki. It adds a whole new layer of depth and mystery to his character, allowing for different interpretations of his powers and his place in the Naruto universe.
One interesting plot twist could be that Naruto has hidden powers that are only awakened when he discovers his true heritage as Kaguya's son. These powers could be something completely different from what he already has, like the ability to control space - time in a unique way.
One interesting otsutsuki fanfiction could be about an otsutsuki who decides to live among humans and tries to understand their emotions. This otsutsuki might start to form relationships with humans, which is a big change from their usual aloof nature.
One possible plot could be that Naruto discovers he has Otsutsuki blood in him. This could lead to him having new and uncontrollable powers that he has to learn to master. He might be shunned by some in Konoha who fear his newfound abilities, while others see it as an opportunity for Konoha to become even stronger. Naruto would then have to struggle with his identity and prove that he is still the same Naruto they know and love.
In the fanfiction, Naruto could enter Kaguya's mind. He might discover her past traumas that led her to become so power - hungry and vengeful. By understanding her pain, Naruto could offer her forgiveness and a new path. He could show her a vision of a future where she is part of a united world, not feared or hated, but respected and loved if she changes her ways. This could be a powerful incentive for Kaguya to change.
Well, Naruto could change Kaguya in the fanfiction by introducing her to the concept of redemption. Given his own journey of facing his inner demons and coming out stronger, he might convince Kaguya that she can atone for her past sins. He may take her on a journey through the ninja world, showing her how people have rebuilt and thrived despite the chaos she once caused. This could make her re - evaluate her actions and change her perspective on the world and her place in it.
First, do your research on the otsutsuki. Know their powers, their appearance, and their general behavior in the original source material. This will help you create a more believable story.