A good way to know is by looking at the writing style. Clear, vivid language and a smooth flow usually indicate a good short story. Also, if it leaves you thinking or feeling something long after you've finished reading, that's a sign it's a good one.
You can tell if it's a short story by looking at its length. If it's relatively brief and focuses on a single incident or a limited set of characters and events, it's likely a short story.
In this fanfic, it might also re - imagine the battles involving Pain. Instead of the battles being just about physical combat, it could explore the psychological warfare aspect more. Pain's abilities, like the Six Paths of Pain, could be used in more creative ways to create a more engaging and different story. It could also focus on how the other characters in Naruto try to understand and counter Pain's complex ideology while dealing with the destruction he causes.
Well, in the original Naruto story, Pain's actions are somewhat more straightforwardly presented as villainous. But in the fanfic, it might humanize Pain more. It could show his past traumas and how they led him to his extreme beliefs and actions.
In many fanfictions, Naruto might use new jutsus or a deeper understanding of his own power. Maybe he taps into a more powerful form of the Nine - Tails' chakra and combines it with his Sage Mode in a unique way to overpower Pain.
You could know the short story by discussing it with others who have read it or reading reviews and critiques. That way, you can gain different perspectives and insights.
In some fanfictions, Naruto's pain might manifest through his actions. For example, he could become withdrawn and isolate himself from his friends. This is because Naruto has always been a social person, so any deviation from his normal behavior could be a sign of his internal pain.
One possible cause could be his sense of failure. Naruto always wants to protect his friends and village, so if he fails in a mission or is unable to save someone, it can cause him great pain.
Mentally, it would be a huge blow to the ninja community. Naruto inspired many with his never - give - up attitude. His death might make some ninjas lose faith in their own abilities and the future. But on the other hand, it could also fuel the determination of some to become stronger in his memory.
His fighting style could become more aggressive. Without the fear of pain, he might be willing to use more extreme techniques that would otherwise be too dangerous because of the pain they cause to the user. He could push his body to the limit more often.