Characterization is key. If the fanfic can capture Naruto's determination and Amaru's special qualities in a believable way, it will stand out. It should also have a well - thought - out plot. For instance, a plot that involves them going on a quest together where they have to rely on each other. This not only shows their bond but also creates exciting storylines. The fanfic could also introduce new elements to the Naruto universe that fit well with the existing lore, like a new type of jutsu related to Amaru's abilities.
In a Naruto Amaru fanfic, what really makes it stand out is the exploration of their emotions. If it can show how Naruto's presence affects Amaru on an emotional level, and vice versa. For example, how they deal with loss or how they support each other during difficult times. The setting also matters. If the fanfic takes place in an unexplored part of the Naruto world, like a hidden village where Amaru has some connection, it can add a lot of intrigue. Additionally, the writing style, if it's engaging and descriptive, can draw the reader in and make the fanfic truly stand out.
A good Naruto Amaru fanfic stands out when it has a unique take on their relationship. For example, if it shows how they complement each other's skills in a new way. Also, if it develops their individual characters more deeply. Maybe Amaru has a backstory that we haven't seen before in the original series, and the fanfic explores that.