At the end of the novel, Carraway celebrates what birthday?

It depends on the context. If it's meant literally as a wife celebrating while naked, it's generally not appropriate in a public or family - friendly setting. However, if it's a more metaphorical use of 'birthday suit' to mean something like being in a natural or unpretentious state while celebrating, then it could potentially be okay, but still a bit strange - sounding.

Well, 'in her birthday suit' is an idiom for being nude. So if there's a story about a wife 'celebrates in her birthday suit', it could be a rather inappropriate or just a very unique and private kind of celebration story. However, it could also be a misnomer and not actually mean being naked at all. Maybe it's a creative way of saying she's celebrating in a very relaxed and unadorned state, like without fancy clothes or something.

Well, typically in the official canon, Harry is not Voldemort's son. Fanfiction, however, allows for all sorts of unconventional storylines. So it's possible in a particular fanfic, but it's not the norm.

No, Nick Carraway isn't depicted as an alcoholic in the novel. He's more of an observant and relatively temperate character.

Nick Carraway is the narrator of the story. His perspective and observations drive the plot forward.

Yes, Nick Carraway does show a tendency to reserve judgment at times throughout the novel.

They are characters in 'The Great Gatsby'.

Definitely. Nick Carraway serves as the storyteller, allowing us to experience the plot through his eyes and thoughts.

Well, it could be about Harry participating in the Beltane celebrations. Maybe he helps with the traditional bonfire, or he could be involved in the Maypole dancing. He might also meet some magical creatures that are associated with Beltane.

Nick undergoes significant growth. He starts as an observer but gradually becomes more involved and gains a deeper understanding of the people and the society around him.