Gray is another character. His ice - magic can complement Natsu's fire - magic. They might team up to fight enemies or overcome obstacles in the way of saving Fairy Tail. Sometimes they bicker while doing so, which adds some humor to the story.
Well, in many of such fanfictions, Natsu might use his unique fire - based magic in really creative ways to save the Fairy Tail guild. For example, he could combine his dragon slayer magic with some unexpected elements from the environment to defeat a powerful enemy threatening the guild.
I'm not sure which specific 'Yuri and Makarov' you are referring to. There could be many characters with these names in different stories. If they are from a game like Call of Duty, Makarov is a very cruel and violent antagonist. Yuri was once his comrade but later turned against him due to Makarov's extreme actions. Yuri finally sacrificed himself to stop Makarov.
Yes, there are some out there. You can start by looking on popular fanfiction websites like FanFiction.net or Archive of Our Own. Some fanfictions might explore unique storylines where Naruto is related to Makarov in this fictional scenario, like Naruto having some of Makarov's magic abilities transferred to him in a cross - over world. However, the quality can vary greatly, so you might need to read a few to find the really good ones.
No, Naruto and Makarov come from two completely different anime series, Naruto and Fairy Tail respectively. In the original stories, they have no relation at all. But in fanfiction, the rules are different. Some fanfic writers might come up with the idea of Naruto being Makarov's father just to mix up the elements from the two series in a very strange and unexpected way. This could be for the fun of it or to explore new storylines that are not bound by the original settings.
He might get seriously injured. For example, he could be poisoned by some magical creature protecting the princess. This would make him weak and in pain but still push through to save her.
In a battle against a group of powerful enemies, Natsu overexerts himself and is on the verge of being defeated. Lucy steps in. She first summons all of her available Celestial Spirits to create a powerful defensive formation around Natsu. Then, she combines her own magical attacks with those of her spirits to drive the enemies away. After that, she uses her healing magic (if she has developed such in the fanfiction) to nurse Natsu back to health.
Well, family is a big theme. Makarov considers the guild members as his family, and in fanfiction, this idea is often explored. For example, how he protects them like a father figure. Also, the theme of sacrifice comes up. Given his position, he might have to sacrifice his own well - being for the guild. And another common theme is the history of Fairy Tail. Makarov has been around for a long time, so his knowledge of the guild's past is often a part of the stories.
One key event could be when Yuri first realizes Makarov's true intentions. Another is when Yuri decides to take action against Makarov. And finally, the moment of their ultimate confrontation.