Are 何でもない and 別に interchangeable?

Question

The way I understand it, 何{なん}でもない and 別{べつ}に are both ways of saying "It's not important", "It's nothing" i.e. brushing off the question being asked. Does this mean that they are interchangeable? Or are there certain contexts where 何でもない is used and 別に cannot be and vice versa?

For example, in episode 19 of Revolutionary Girl Utena, the character Wakaba is asked by another character "Why do you keep accusing me of [being a player]?" to which she starts to reply, but then decides against it, saying "別に...何でもない" and turns away. In this context, she uses both, which makes me think that she uses both as a way of reinforcing "It's not important", which makes me think that both expressions have similar meaning and are therefore interchangeable.

Answer 1

別に is an adverb and 何でもない is an adjective expression. They can both be used on their own to mean something that an English speaker understands from "it's not important".

They are not interchangeable though, first of all for their part of speech difference and their meaning also changes with context. 「別にいい」 means "it's okay" and 「完璧でも何でもない」 means "not perfect or anything".

In 「別に…何でもない」 their meaning can reinforce each other, but it depends on intonation and pauses what was actually meant. In 別に the meaning of something not being important is only implied, so it is possible that 何でもない confirms the implication.