The plot could involve Kakuzu being controlled by a more powerful and evil force. Naruto, after trying to reason with him and failing, has no choice but to kill him. This could also be a part of Naruto's growth, where he realizes that sometimes, in the face of extreme evil, killing is the only option to protect others.
Kakashi could be a significant supporting character. He could provide Naruto with some advice or even join the battle alongside Naruto for a while. Another possible supporting character could be Hinata. Her gentle presence and belief in Naruto could give Naruto the extra motivation he needs during the fight.
One possible plot could be that Kakuzu, with his tough and practical nature, trains Naruto in a very different way from the traditional Konoha style. He might focus more on self - reliance and survival skills. Naruto could learn unique jutsu from Kakuzu related to his earth and water - based techniques.
In such a fanfiction, perhaps Kawaki is driven by some extreme ideology. Maybe he believes Naruto's way of peace is a weakness and decides to take him out to change the ninja world in a more radical way.
Maybe the plot involves a mission where Naruto is sent to a realm that has been invaded by goblins. The goblins have a powerful magic item that they are using to gain an upper hand. Naruto has to fight his way through hordes of goblins, using his various jutsus like the fireball jutsu to clear paths. Along the way, he discovers the goblins' weakness and finally manages to kill the main goblin force, saving the day in this strange new world.
In a 'Naruto kills Gato' fanfiction, the plot could start with Gato's continued oppression in the Land of Waves. Naruto, having witnessed the suffering of the villagers, decides he's had enough. He uses his Shadow Clone Jutsu to surround Gato and his men. With a swift combination of Rasengan and his ninja skills, he takes Gato by surprise and defeats him, thus liberating the Land of Waves in a more direct and violent way compared to the original story.
In the 'kushina kills naruto fanfiction', perhaps there's a misunderstanding that leads to this extreme situation. For example, Naruto could be framed for something really bad, and Kushina, believing the false information, takes drastic action. It's a really twisted concept compared to the original story where family is so important.
One possible plot could be that Zeus somehow gets involved in the Naruto universe and starts causing chaos. Naruto, being the hero, decides to take him on. He could use his shadow clone jutsu to confuse Zeus and then land a powerful Rasengan on him. Maybe Zeus underestimates Naruto's abilities and is caught off guard, leading to his defeat.
Maybe a dark force takes over Naruto's mind. This force could be an ancient evil that has been sealed away for centuries and now wants to create chaos in the ninja world. It uses Naruto as a puppet to kill Tsunade, one of the most powerful protectors of the village. The story could then focus on Naruto's friends trying to free him from this control and avenge Tsunade.
One possible reason could be a power struggle. If Riser somehow poses a threat to Naruto's world or his friends. Naruto, being the protector, might take extreme measures. For example, if Riser was trying to take over Konoha or steal some important ninja art. Naruto would fight to defend his village and in the heat of battle, end up killing Riser.
One possible plot could be that Naruto is somehow corrupted. Maybe he's been influenced by a powerful dark force or a powerful enemy has tricked him into believing that everyone is a threat to the world he wants to protect. So, he decides to take extreme measures and kill everyone to 'create peace' in his warped sense.