In this fanfiction, it could be that the pressure of being 'The Chosen One' finally gets to Harry. All the battles, the losses he has endured, and the constant threat of Voldemort might push him over the edge. He could start acting erratically, pushing away his friends and allies because he no longer trusts his own judgment.
One possible plot is that a cursed object finds its way to Harry. This object slowly corrupts his mind. As his mind starts to go, he begins to make decisions that are out of character. For example, he might start to side with the Death Eaters or abandon Hogwarts, thinking that it is the only way to end the war. His friends would then be faced with the difficult task of trying to save him without knowing exactly what is wrong.
In this fanfiction, there could be a villain who has the ability to manipulate Naruto's mind. The villain might use this power to make Naruto turn against the Hidden Leaf Village. Naruto, without control of his own mind, could start causing chaos within the village, like attacking important buildings or trying to steal important ninja secrets.
Well, it could start with Harry being lured into a trap by some mysterious enemies. They might be after the secrets of Dumbledore's Army or something. Once trapped, they start torturing him. His glasses could be lost when he's thrown around during the torture. Then, he might use his magical skills, like his ability to communicate with snakes (which he has from being a Parselmouth), to call for help or find a way to escape. He'd be at a disadvantage without his glasses, but his determination would keep him going.
One possibility could be that Harry is cursed by a dark wizard. This curse slowly drains his magic, causing him to struggle with everyday wizarding tasks. He might have to rely more on his non - magical skills and the help of his friends. For example, Hermione could use her vast knowledge to find a way to reverse the curse while Ron provides emotional support.
In 'Harry Loses His Emotions Fanfiction', it could be that Harry experiences a really traumatic event. Maybe he witnesses the death of a very close friend in a battle. This shock is so great that it makes him shut down his emotions as a self - defense mechanism. He then becomes cold and distant, and the story could be about how his friends struggle to reach the old Harry again and help him heal.
Maybe in the fanfiction, Harry's twin could be lost in a magical accident. For example, during a wizarding battle, the chaos causes them to be separated, and Harry spends the rest of the story trying to find his twin.
Well, in the 'Harry Potter loses his magic fanfiction', he could end up finding new strengths within himself. Maybe he discovers that his courage and intelligence are enough to get him through tough situations even without magic. He could also start to see the wizarding world from a different perspective, one of the non - magical people, and perhaps work towards making the two worlds more inclusive.
One possibility could be that after facing too many losses, like the deaths of his friends in the fight against Voldemort. For example, if Hermione and Ron were killed right in front of him during a final battle. Harry might feel that all his efforts were in vain and lose the will to live. Another reason could be that he discovers some dark secrets about the wizarding world that shatter his beliefs. Maybe he finds out that Dumbledore had some truly evil intentions all along and that everything he fought for was based on a lie.
A new, unknown villain could be the cause. This villain might have a special power related to mind control or mental manipulation. They target Naruto because of his status as a hero in the ninja world. By making Naruto lose his mind, they could throw the entire ninja world into chaos.
It could also be due to a choice Harry makes that his friends don't agree with. Suppose Harry decides to take on a very dangerous mission alone to protect his friends, but they see it as him not trusting them. This could lead to a rift and eventually him losing their friendship.
In the fanfiction, when Harry Potter loses his glasses, it could lead to some really interesting character development. For example, his friends might have to step up and protect him more. Also, it could be a chance for him to discover new magical ways to improve his vision without the glasses, perhaps a spell or a potion that he has to search for.