For Neji, he could develop more of an emotional side. In the original series, he was often stoic. In fanfiction, he might open up more, especially to Tenten. Maybe he starts to show his sense of humor or his fears. For Tenten, she could become more confident in her abilities. She's always been a strong fighter, but she might gain the confidence to take on more leadership roles within their team.
One idea could be a story where Neji and Tenten go on a special mission together. They face many challenges and in the process, Neji discovers a new side of Tenten's strength. Maybe she uses some unique weapons or techniques that Neji has never seen before, and he gains a new respect for her.
Sure, Naruto Shippuden has a manga. The manga provides the original story and inspiration for the anime adaptation. They share many key plot points and character developments.
In many fanfictions, Naruto might use his unique chakra, perhaps enhanced by his Uzumaki heritage or the Nine - Tails' power. His strong will and connection to his friends could also play a role, allowing him to find a way to break the seal through sheer determination and his belief in Neji's potential.