Power imbalance could also be a reason. If Naruto's power suddenly goes out of control or he misjudges the Teen Titans' power levels and thinks they are a danger to his world or friends, he might take extreme actions. For example, if there's some kind of power - up in Naruto that makes him overly confident or paranoid, he could lash out at the Teen Titans thinking he's protecting something important.
One possible reason could be that the council has been secretly plotting against Naruto all along, perhaps trying to undermine his power or even get him exiled. Naruto might have discovered their malicious plans and decided to take pre - emptive action to protect himself and his friends.
It could also be due to a misunderstanding. In the heat of the moment during the vote, there might have been miscommunications or false assumptions. Naruto might have thought Sasuke was going to betray them all and in his haste to prevent that, made the tragic decision to kill him.
It could also be that the situation was extremely dire. For example, the troll was about to destroy something very important, like a magical artifact that could cause great harm if it fell into the wrong hands, and Hermione saw killing the troll as the only way to prevent that.
One possible reason could be extreme pressure. The Chunin Exams are highly competitive and Naruto might have felt that he was constantly failing and disappointing those who believed in him. Maybe he saw no way out of the situation and in a moment of despair, decided to end his life.
Another reason could be for disguise. Naruto might be in a situation where he needs to hide his identity. By covering his eyes, which are a very recognizable feature of his, he can make it more difficult for others to figure out who he is. This could be especially important if he is in enemy territory or trying to infiltrate a group secretly.
Well, Naruto could bring his unique ninja skills to the Teen Titans. His Rasengan could be a powerful new attack in their arsenal. Maybe he'd teach them some of his chakra control techniques too.
There are so many fanfictions out there, and while the idea of 'Naruto kills Teen Titans' is quite a unique and probably controversial concept in fanfiction, without actively searching through specific fanfiction sites, it's hard to find and describe. Fanfiction often takes creative liberties and can have very different interpretations of characters and their actions.
Yes, such fanfictions exist. In these fictional scenarios, Naruto might kill himself because of Sasuke for several reasons. Naruto's whole life has been centered around Sasuke to some extent. If he feels that he has failed in his mission to bring Sasuke back to the right path and that the situation has become so dire that the only way to atone for his 'failure' is through his death, he might do it. Also, if Sasuke were to cause harm to someone Naruto holds dear, like the village or his other friends, and Naruto feels powerless to stop him in any other way, he could choose to end his own life as a last resort.
One possible reason could be a miscommunication that escalates out of control. Maybe Sasuke is on a path that Naruto believes is too dangerous for the world, and Naruto, in an attempt to stop him, accidentally kills him. For example, Sasuke might be about to use a powerful and uncontrollable jutsu that Naruto fears will destroy the Uchia compound and much more, so he acts in haste.
If such a fanfiction exists, one possible reason could be a mind - control situation. Maybe an enemy uses some powerful genjutsu to make Naruto believe his sister is a threat, causing him to kill her accidentally. Another reason could be a misinformation plot where Naruto is tricked into thinking his sister has committed some unforgivable crime against the village.