I'm not sure specifically as there could be many different interpretations of such a fanfiction. It might be about Harry in a situation where he has to give himself stitches, perhaps after getting injured in a dangerous adventure, like a battle in the wizarding world.
Obviously, Harry would be the main character. But there could also be other characters involved in the events leading up to him having to give himself stitches. For example, his friends like Ron and Hermione might have been there before and left him in a situation where he got injured.
There might be a lot of such fanfictions out there. However, to find them, you need to use effective search terms. Maybe adding the name of the source material (if it's based on a particular movie, book, etc.) to 'Peter gives himself stitches fanfiction' in the search bar would help. For example, if it's related to a superhero story, adding the superhero's name.
Another theme could be pain and endurance. Stitching oneself is a painful process, so the fanfiction might explore how Peter endures this pain and what it says about his character. It could also show his determination to keep going despite the injury. Usually, in these stories, there's also a sense of secrecy or isolation, as he might be stitching himself up alone, away from others for some reason.
One good 'Peter stitches himself' fanfiction might be found on popular fanfiction platforms like Archive of Our Own. You can search using relevant tags such as 'Peter' and'stitches' to narrow down the results.
Hermione would be devastated. She would initially think Harry had lost his mind. She'd probably try to find a way to rescue him, using all her knowledge and research skills. Ron would be angry at first, feeling that Harry had betrayed them. But then he would also start to think there must be a deeper reason and would want to help. Dumbledore, if still alive in the fanfiction, would likely be more understanding, believing that Harry has a grand plan that he's not aware of yet.
One plot idea could be that Harry gives himself to Voldemort in an attempt to understand the Dark Lord's mind and find a weakness from within. Another could be that he sacrifices himself this way to protect his friends and Hogwarts, believing that there's a way to turn Voldemort's victory into a defeat from the inside. Or perhaps Harry has a vision that shows this as the only way to truly end the war and he decides to take the risk.
One possible plot could be Naruto believing that by joining the Akatsuki, he can change them from the inside. He might think that his influence can stop their more evil plans. For example, he could try to convince them to stop collecting the tailed beasts in a violent way.
Perhaps he's dealing with some sort of trauma. For example, after the many battles he's been through, like the fight against Voldemort, he may be suffering from post - traumatic stress disorder. To cope with this, he isolates himself from others as he doesn't want to burden them or he's just too caught up in his own dark thoughts.