One possible plot could be that Hinata discovers she's having a baby unexpectedly. This throws her life into chaos as she has to balance her personal life, relationships, and her own growth. Maybe she struggles with how to tell the father, if there is one in the story, and she also has to deal with the reactions of her friends and family.
Perhaps the baby could be named Kazuki. It gives a sense of being strong and noble, which would be fitting for the child of Naruto and Hinata. In fanfiction, the name could also be symbolic of a new beginning or a special power that the baby might possess, like being related to the combination of Naruto's Nine - Tailed Fox power and Hinata's Byakugan abilities.
Friendship can also be a key theme. Even as a baby, she could start to form bonds with future teammates or friends. Fanfics might explore how these early relationships influenced her development and her love for the sport. For instance, a childhood friend who inspired her to keep going in volleyball.
The baby might inherit Naruto's ability to use chakra in large amounts and his signature Rasengan. Since Naruto has such a vast amount of chakra, it's likely that his child would also have a significant chakra reserve.
Hinata's family would also have to deal with the emotional aspect. They love Hinata in her normal state, and now they have to adjust to this new form. They might start to remember when Hinata was actually a baby before and all the hopes and dreams they had for her then. Some of the more conservative members of the family might be more hesitant to let Naruto be around her, but the more open - minded ones could see that Naruto's presence is actually good for her in this state. And they would all be united in their goal to get Hinata back to her normal self.
One common theme is the origin of his love for volleyball. Since he's depicted as a baby, authors often explore how that initial interest in the sport might have started. It could be through seeing an older player or just having an inborn passion for it.
In this fanfiction, it could be that Hinata's memories are still somewhat intact even as a baby. So she might still show signs of her shyness towards Naruto. She could blush when Naruto gets close to her while taking care of her. And perhaps, this situation could lead to Naruto realizing his deeper feelings for Hinata in a more protective and caring way. He would start to see her in a different light and understand how important she is to him on a whole new level.
Hinata and Naruto's baby was like a little ray of sunshine in their lives. The baby girl had a special charm. Hinata took great care in dressing her up in cute little outfits. Naruto was a doting father, always carrying the baby on his shoulders. One day, when the baby took her first steps, it was a moment of pure celebration. Hinata and Naruto held hands, watching their daughter with pride. Their baby brought out a new side of them, a side filled with even more love and tenderness.