In the fanfiction, it might be that Naruto and his sister are in a competition. Naruto, with his determination and experience from his adventures, manages to beat his sister. This could be a physical competition, like a race, or it could be a more mental one, like solving a difficult ninja - related riddle faster than her.
Perhaps in this fanfiction, his sister has done something wrong or dangerous, and Naruto has to 'beat' her in the sense of stopping her. It could involve a moral or ethical conflict within the story that Naruto has to resolve by overpowering his sister's actions.
She could be an original character created specifically for this fanfiction. The author might give her unique abilities and a distinct personality to make the story more interesting.
Maybe Sakura gets angry at Naruto for some misunderstanding, like he accidentally ruins one of her important medical experiments. So she decides to beat him up to teach him a lesson.
I haven't actually read this specific fanfiction, but generally, it might involve Naruto using his ninja skills like shadow clones, rasengan, and his high - speed movement abilities to take on the powerful members of the Justice League. Maybe he uses his chakra to counter their superpowers.
Well, in such a fanfiction, perhaps Sasuke has some sort of plan that involves Hinata in a negative way. Naruto discovers this and decides to beat up Sasuke to protect Hinata. It could also be part of a bigger struggle where Sasuke's actions are seen as a threat to the future Naruto envisions with Hinata, so Naruto takes matters into his own hands to stop him.
A plot could involve a common enemy that threatens both the world of Angel Beats and the Naruto world. The Akatsuki from Naruto might be interested in the powers that exist in the Angel Beats world. So they start to invade it. The characters from both sides would have to team up. Naruto and Otonashi would lead their respective teams. Hinata could bond with some of the female characters in Angel Beats over their shared experiences of having to be strong in difficult situations. And Kakashi could teach some of the Angel Beats characters some ninja techniques.
Well, in a way it depends on the context of the fanfiction. If the writer decides to give Naruto some sort of super - powered boost or if Jiraiya is weakened in some way. For example, if Naruto has some unique power - up that allows him to counter Jiraiya's toad - related jutsus easily. But Jiraiya is a very experienced and powerful shinobi too, so it's not a straightforward win for Naruto without some plot devices.
The plot could start with a tournament - like scenario where Naruto and Neji are pitted against each other. Naruto is tired of Neji's overconfidence and decides to teach him a lesson. So he goes all out from the start and uses his unique ninja skills to overwhelm Neji.
One possible reason could be a simple rivalry that has boiled over. Maybe they were competing for the same mission, and Naruto's determination to prove himself got the better of him. He might have seen Kiba as a threat to his goal of becoming Hokage, thinking that if Kiba succeeds in a high - profile mission, it could overshadow his own achievements.
One possible reason could be a misunderstanding. Maybe Sakura makes a decision that Naruto strongly disagrees with regarding the safety of the village or their friends. For example, if Sakura decides to trust an enemy without Naruto's knowledge, Naruto might get so angry that he lashes out at her.
Maybe Naruto has discovered a new powerful jutsu that Kakashi isn't aware of. This gives him an edge in the fight and he manages to defeat Kakashi.