One possible reason could be the overwhelming pressure. In the BNHA world, Izuku faces a lot of high - expectations. If he constantly fails to meet them, he might give up. For example, if he fails to control his newfound power or if he keeps getting injured during battles, it could lead to a sense of hopelessness. Another reason could be the loss of important people around him. If he loses someone like All Might, who is a huge inspiration for him, he might lose the motivation to keep going.
Perhaps the constant danger and the realization of the true cost of being a hero could make him give up. Every time he goes into battle, he risks his life. If he witnesses too much death and destruction, or if he himself has a near - death experience that makes him realize how fragile life is, he may think that the price of being a hero is too high and choose to abandon his dream.
He might give up because of self - doubt. Izuku started as a quirkless hero - in - training. Despite getting a quirk later, he might still have deep - seated insecurities. If he starts to believe that he's not worthy or capable of being a hero, like if he compares himself too much to his more naturally talented classmates, he could decide to give up. Also, if the society in BNHA turns against him, for instance, if there are false accusations against him, it could break his spirit.
One possible reason could be that Izuku realizes Bakugou's unchanging and hostile attitude. Despite his efforts to be friends or get along, if Bakugou continuously rejects him or is overly aggressive, Izuku might feel it's a lost cause.
If Izuku gives up, his friends like Ochaco would be deeply affected. Ochaco has always been inspired by Izuku's determination. Without him, she might lose some of her own motivation. Bakugo too would be impacted. Despite their complex relationship, Bakugo has come to respect Izuku's growth. His giving up could be a shock to Bakugo and might even make him re - evaluate his own path as a hero.
Another aspect could be the general discrimination in the BNHA society. The fact that society is so focused on quirks and those without are often looked down upon might have made Izuku bitter. He could be hating everyone because he sees the society as a whole being corrupt and unkind, not just the individuals who directly wronged him.
The fanfic might be special because of the new relationships it creates for Izuku. Maybe it pairs him with characters in unexpected ways, which can lead to interesting storylines. For instance, if it has Izuku form a strong bond with a villain - turned - ally, it would add a whole new layer to the BNHA universe.
Maybe Naruto gets tired of always chasing after Sasuke. He has his own life and dreams too. He might think that he has sacrificed enough of his time and energy on Sasuke, and it's time to focus on himself and the village. He could start to believe that Sasuke has made his own choices and he can't keep forcing Sasuke to come back.
It might be that Ash has other priorities now. For example, real - life commitments such as work or study have taken up too much time, leaving no room for writing fanfic.
One reason could be the sacrifices he has to make for the village. Naruto is so dedicated to protecting Konoha that he might feel he doesn't have time for love. His responsibilities as Hokage are immense, and he has to constantly be on guard against threats. Another reason could be past traumas. He has lost many people he cared about, like Jiraiya. This could make him afraid of getting close to someone again and losing them, so he gives up on love.
It could also be due to a misunderstanding. Some false information might have spread in the fanfic's world, making Naruto believe that everyone has turned their backs on him. Like, some bad guys framed his friends, and Naruto, being unable to see through the lies at first, gives up on everyone in despair.
Maybe the loss of a very dear Pokémon friend. If something bad happened to a Pokémon he was extremely close to, like it getting seriously injured or lost forever, it could be so devastating that he loses the will to continue his journey and thus gives up.
It could also be that he is tired of the false expectations created by fanfiction. In fanfiction, his character might be portrayed in ways that don't match who he really is. He wants to be true to himself and his ninja way, so he gives up fanfiction.