One possible reason could be extreme emotional distress. Maybe she feels like she has failed Sasuke in some way, like not being able to save him from the darkness, and she self - harms as a form of punishment. Another reason could be in a situation where she has to make a sacrifice. For example, if Sasuke is in danger and her cutting off her arm is the only way to activate a certain power or jutsu to save him.
It could make Sasuke more protective of Naruto. Sasuke has always had a complex relationship with Naruto, and seeing him lose an arm would stir up some deep emotions. He might feel guilty, especially if he was somehow involved in the incident that cost Naruto his arm. This could lead to Sasuke staying closer to Naruto and being more open about his feelings.
Well, I'm not sure of a specific one off the top of my head. But you could try searching on fanfic websites like Archive of Our Own. Just type in 'Sakura cutting arm Sasuke fanfic' in the search bar and browse through the results. There might be some really interesting ones there.
I recommend " The Female Supporting Character's Buddhist Counterattack." Although the plot was different from the novel described in the question, it was all about the female protagonist's counterattack. The female protagonist of this novel had also been transmigrated into the book, but she did not want to follow the original plot. Instead, she planned to counterattack successfully. There was also a sweet interaction between the male and female protagonists in the story. Moreover, the female protagonist also had a specialty--playing the piano. The male protagonist burned the female protagonist's hand, but the female protagonist still broke through the predicament in the competition and succeeded in going solo. I hope you like my recommendation.
I recommend the following novels to you: " The Rebirth of the Apocalypse: The Bio-Experimental Vanguard ": The protagonist has the ability to fuse biochemical genes without limit, surpassing the peak of the life of the Tyrannical Star in the apocalypse. 2. [Bio-Hegemon: The protagonist has been reborn in the apocalypse and has become the spokesperson of the counterattack.] 3. < Reborn 100,000 Years Later >: The female protagonist, Yi Chen, was reborn 100,000 years later. She was identified as a Qilin cub and became the only Qilin. This book is a wonderful oriental fantasy novel. If you like the female protagonist's rebirth and the elements of Qilin, this book should suit your taste very well.
The tattooed half of the arm referred to the tattoo area from the shoulder to the elbow. There were various designs and styles that could be chosen for this area, including a Japanese half-skin tattoo, half-armor tattoo, and a flower arm tattoo. Half arm tattoos usually appeared in a symmetrical form, and the appropriate pattern and style could be chosen according to personal preference and the tattoo artist's suggestion. In tattoo design, the half-arm tattoo often followed the law of composition, cleverly using light and dark, dense distinction to contrast the theme pattern. There were some differences between the tattoos on the arms of boys and girls. The tattoos on the arms of girls usually did not extend to the chest, while the tattoos on the arms of boys could extend to the chest or shoulder. In short, a half-arm tattoo was a common tattoo. Choosing the right pattern and style could show a person's unique style and personality.
Sasuke could be a candidate. Given their complex relationship, Sasuke might find a way to give Naruto a new arm as a way to atone for their past differences. He could have discovered some rare medical ninjutsu during his travels or come across a powerful artifact that he uses to create a new arm for Naruto.
Maybe Orochimaru. Despite being a villain in the past, he is a master of forbidden jutsus and experiments. He could see Naruto as an interesting subject and give him a new arm with some dark powers, which Naruto would then have to learn to control for the greater good.
Well, it could be that he got it as a gift from some super - advanced ninja technology group in the fanfiction world. Maybe they saw his need for an extra weapon or tool during battles and decided to equip him with a metal arm.