In the 'harry shows his power fanfic', perhaps it's a story where Harry has to show his power in a wizarding competition. He might use his unique abilities like Parseltongue to outwit his opponents and prove his worth. He could also draw on his connection with the Patronus charm to protect himself and others during the tasks.
There are fanfictions where Naruto's power is shown through his ability to connect with the spirits of past Hokages. With their combined wisdom and his own strength, he's able to perform a super - powerful jutsu that not only protects Konoha but also restores the balance of the ninja world. He uses this new - found power to face an ancient evil that has been awakened.
In this fanfic, Harry is the main character. However, we could also expect to see Dumbledore making an appearance. Dumbledore has always been a guiding figure for Harry, and in a story about Harry showing his power, Dumbledore might offer some wisdom or crucial information. Neville could also be a key character. He has his own growth in the original series, and in this fanfic, he could be inspired by Harry's power and contribute to the overall plot in some way.
Well, Goku's power level progression could be different in that he might be more in control of it. Since the head injury had some impact on his psyche, without it, he could have a more calculated approach to increasing his power. He might not rely as much on the Kaioken technique, which was developed in part due to his need to overcome limitations caused by his injury - affected development. Instead, he could focus more on pure Saiyan power - up methods like the Great Ape transformation and evolving it further.
One common scenario is when Percy is forced to go on yet another dangerous quest without much support from the gods. He might be angry and show his hatred at that moment. For instance, if he is sent to retrieve some powerful artifact with very little information and no real backup from the gods.
Well, Naruto could show Boruto his Sage Mode power. Sage Mode gives Naruto enhanced strength, speed, and the ability to sense chakra more acutely. It's a very powerful form that Naruto has mastered over time. By revealing it to Boruto, he might be teaching Boruto about the different levels of power and the hard work required to achieve such power.
One trait is his love for combat. Goku would constantly seek out strong opponents to test his skills. Another is his Saiyan pride. He might not back down from a challenge even if it seems impossible. Also, his Saiyan appetite. He would probably eat huge amounts of food to fuel his Saiyan - level energy.
Goku in the manga doesn't hit a power level of 8000. The power escalation in the story doesn't go that high for him. There are various factors and story arcs that determine his power growth, but 8000 isn't one of them.