Yes, it can be. Naruto is typically seen as a hero with strong values in the original series. Portraying him as a 'killing machine' goes against his character's essence, which might be disturbing to many fans who love the positive aspects of Naruto's personality.
It could be due to a great tragedy. For example, if all his friends were killed and he was filled with rage and revenge. In that state of mind, he might become a killing machine, just focused on destroying those who wronged him.
The Naruto as a killing machine in fanfiction changes the narrative in multiple ways. First, his character development would take a very different path. Instead of growing through friendship and hard work, he would be shaped by violence. Second, the story's themes would shift from positive ones like perseverance to darker ones like power and destruction. Third, the other characters would have to adapt to this new Naruto, which could lead to new alliances and conflicts. It's a huge departure from the original Naruto story.
Some creators might want to explore a darker side of Naruto's character. Maybe they're tired of the always - positive and heroic Naruto and want to see what he'd be like if pushed to the extreme.
It's not really that common in the overall fanfiction world. Fanfiction often leans more towards relationship - building, exploring different character arcs in a more positive or complex way. But for those who like a more out - there and action - packed take on Harry, it could be a thing. There are so many different types of fanfiction out there, and this is just one of the more unusual ones.
One possible plotline could be that Harry is somehow transformed into a killing machine against his will. Maybe he's under a dark spell or some sort of mind control. And he has to fight against this new - found, violent nature while also dealing with his friends who are trying to save him.
In some fanfictions, Naruto could potentially be depicted as a 'war machine'. Fanfiction often takes creative liberties with characters. Some authors might explore a darker or more militaristic side of Naruto, where his powers are used in a very aggressive, war - like manner. However, this is a departure from his more typical characterizations in the original series.
Yes, there might be. The Naruto fandom is vast and creative, and it's not uncommon for fans to create crossovers like this. You can try searching on popular fanfiction websites such as FanFiction.net or Archive of Our Own.
One possible scenario in this fanfiction could be that Naruto's power is harnessed in a more militaristic way. Maybe due to some dark forces threatening the ninja world, Naruto is turned into a 'war machine' not by choice but by necessity. Yugito might play a role in either trying to bring back the old Naruto or helping him control this new, more violent side of himself.
It changes the fundamental nature of the character. Naruto is typically a symbol of hope and friendship, so making him like killing makes the story much darker and less inspiring.