It could be because of a serious injury or illness that affects their abilities. Or perhaps they lost their motivation and drive, leading to a decline in their talent.
Could be that they faced a powerful enemy or adversary who managed to suppress their talent. Another possibility is that they made a mistake or wrong choice that had long-lasting negative effects on their skills.
Maybe it's due to some sort of curse or evil magic. That's a common trope in manga.
Perhaps there was a misunderstanding between them. The black cock might have said or done something that his girlfriend misinterpreted, and without proper communication to clear things up, the relationship deteriorated and she left him.
Maybe it was due to a fierce battle. The enemy could have targeted the equipment related to his wings, like shooting down the vehicle or device that supported the wings' function.
One possible reason could be the loss of his friends. Naruto deeply values his relationships, and if something were to happen to his friends like Sasuke leaving again or getting seriously injured, it would shatter his happiness. Another reason might be if he fails to protect the village. Naruto has always seen himself as the protector of Konoha, so if he fails in this duty, his sense of purpose and happiness would be lost.
Another reason might be related to a plot device in the fanfiction. The author could be using the loss of the mask to create a turning point in the story. It might lead to new relationships being formed or old ones being tested. For instance, his friends might react in different ways when they see his face without the mask, and this could drive the story in different directions.
One reason could be betrayal by his friends. For example, if someone he considered a close ally made a deal with his enemies behind his back, it would shatter his trust. Another might be lies from the village leaders he respected. If they hid important information or manipulated him for their own gains, Naruto would start to question who he could trust.
If someone were to insult or harm Hinata, who he loves deeply, Naruto could lose his temper. He's very protective of those close to him, and any threat to Hinata would likely trigger his anger. He has a strong sense of justice and loyalty, so seeing someone he cares about being mistreated would be a big deal.
Yes, Deku loses One For All at a certain point in the manga.
She could be running too fast, like in a race or just being playful. For example, if she was playing tag with her friends, her shoes might come off as she dashes around.
Yes, Ichigo does lose his powers at some point in the manga.
Yes, he does. This event has a major impact on his character's journey and the story's progression. It leads to new challenges and growth for Deku.