Captain America would probably be very reflective. He might see his past self as a reminder of his long journey and how much he has changed. He could try to offer some words of wisdom to his younger self.
Some gods might be entertained. For instance, Hermes, being the trickster god, might enjoy seeing the different and often humorous takes on the gods in the fanfiction.
The main differences are in their expressions and some minor details of personality. In the manga, Deku might seem a bit more intense, while in the anime, he's sometimes presented a bit softer.
Boruto might be in awe. He has always known his father as the Hokage, a powerful and respected figure. Seeing Naruto's past full of struggles, loneliness, and determination would make him realize how far his father has come. It could also make Boruto more empathetic towards Naruto and perhaps inspire him to be more like his father in some ways.
Rapunzel would probably be very curious. She might see the ghost as another adventure or a chance to learn more about herself. Since she has such an open - minded and positive attitude, she would likely follow the ghost willingly and be eager to see what the past has in store for her to discover.
Issei could be a bit nervous at first. He might worry about what his classmates will think. But if they show positive reactions, he could become more confident and start sharing more about his writing. However, if they react negatively, he may feel a bit down and might even regret that they saw it.
Well, obviously Deku in two forms - the younger and the older version are the main characters. The younger Deku is the one who is still growing and learning, while the older Deku has more experience.