Well, it depends on the specific fanfiction. There are numerous fanfictions out there with different interpretations of Naruto. Some might focus on his regular ninja skills and not turn him into a super soldier, but in others, he could be given super - strength, super - speed, and other qualities typical of a super soldier to make for an interesting and unique story.
His speed is another characteristic. Naruto could move at blinding speeds, making it almost impossible for opponents to track him. In some fanfictions, he can zip around the battlefield so fast that he appears as a blur, dodging attacks effortlessly and launching his own counterattacks in an instant.
In this fanfiction, Naruto might have the same kind of combat skills as the Winter Soldier. He could be stealthy and efficient in combat, using his ninja skills in new and unexpected ways. For example, his shadow clones could be used to create distractions like the Winter Soldier's misdirection tactics. And his journey to break free from the control that has been imposed on him would be an interesting plot point.
One common theme is transformation. Naruto often transforms from a regular ninja into a more disciplined soldier, which brings about changes in his behavior and relationships. Another theme is loyalty, as he has to show loyalty to his new military - like group.
It's possible that there are other original characters created for the fanfiction as well. For example, there could be a mentor figure for the soldier of fortune, someone who has been in the business of being a soldier for a long time and imparts their wisdom and skills to the main character. Or there could be a rival soldier of fortune who is constantly trying to outdo the main character in various missions and challenges.
Another theme is the struggle for identity. When Naruto is a child soldier, he may question his purpose and who he really is. Is he just a weapon for the village, or is there more to him? This internal conflict can be a major part of these fanfictions.
One interesting plot could be a story where the main character, who is a soldier of fortune in the Naruto world, gets involved in a mission to protect a hidden village from a new and powerful enemy. This could involve lots of action and strategic battles.
Some 'Naruto child soldier fanfiction' delves into the political aspects that led to the creation of child soldiers in the Naruto universe. It could show how different villages' power struggles and lack of resources might have forced them to use children in combat, and Naruto's journey to change this situation.
Naruto himself is often very popular in these fanfictions. His energetic and determined personality makes for interesting crossovers. He can bring his ninja spirit to the Rune Soldier world and interact with the characters there in unique ways.
One interesting Naruto Rune Soldier fanfiction could be about Naruto being transported to the Rune Soldier world and having to adapt to its magic system. He might use his ninja skills in unique ways combined with the rune magic there.