Well, it could be due to the weight of expectations. Naruto is often seen as the 'chosen one' type of character. In fanfic, Sasuke might feel pressured by this. He might think that no matter what he does, he'll always be in Naruto's shadow. Also, their different upbringings play a role. Naruto grew up alone but with a positive attitude, while Sasuke had a tragic family past. In fanfic, seeing Naruto's strength despite his hardships could make Sasuke question his own strength and lead to depression.
In fanfiction, Naruto could be depressed after the war because he realizes that the world he fought for is still full of problems. The shinobi system might still be corrupt in some ways, and he may feel that all his efforts haven't really changed the fundamental issues. He might also be suffering from post - war stress disorder, constantly reliving the battles and the horrors he witnessed.
One reason could be his sense of isolation. In many fanfictions, Merlin might feel alone as he has to keep his magic a secret from most people around him. This constant hiding and fear of discovery can lead to depression.
One possible reason could be his deep connection with Naruto in the original story. Fanfiction might offer new and different perspectives on their relationship, which intrigues him. Maybe he wants to see how others interpret their bond, whether it's their friendship or the complex rivalry. Another reason could be that fanfiction allows him to exist in scenarios that didn't happen in the official storyline, giving him a chance to explore different aspects of his character and his interactions with other characters.
In such a fanfic, one possible reason could be Naruto's feeling of being left out. Maybe he sees Sakura's constant focus on Sasuke and feels neglected in their friendship triangle. Another reason might be jealousy. If Naruto has unrequited feelings for Sakura, seeing her love for Sasuke could turn to hatred over time.
In some fanfics, Naruto may be sad because of unrequited love. He has strong feelings for someone, but that person doesn't return his feelings. Naruto is a very emotional character, and love is an area where he can be easily hurt. So this could be a source of his sadness in the fanfic.
One reason is that Naruto has the Nine - Tails' chakra. In fanfic, this power can be further enhanced or manipulated in ways that make him far more powerful than Sasuke. Another reason could be his more outgoing personality. He might be able to form alliances more easily, leading to him having more resources and power - ups at his disposal.
One reason could be Naruto's power. In the Naruto universe, Naruto has great power, and both Itachi and Sasuke might see Naruto as a key to achieving certain goals. Itachi might want to protect Naruto because he sees Naruto as a force for good in the future of the ninja world. Sasuke, on the other hand, may view Naruto as a rival in terms of power and influence, and in fanfiction, this could lead to a fight between them over Naruto.
A moment of desperation. For example, if one of them is about to die in the alley due to an injury or a curse. The other, in a rush of emotion, kisses them as a way to convey all the unsaid things, all the love and friendship that has been there all along.
One reason could be to create a lot of angst. If Sasuke cheats, it would deeply hurt Naruto and cause a rift in their relationship, which could lead to a lot of emotional turmoil for both characters. This would make for a very dramatic story.
One reason could be the constant threat to the world in the Dragon Ball universe. She might feel helpless as a non - fighter, seeing her friends and family in danger all the time. For example, when powerful villains like Frieza or Cell were on the loose, she could be depressed about her inability to contribute more directly to the fight.