In Kyoukai no Kanata, are youmu the same as youkai?

Question

In Kyoukai no Kanata, are youmu the same as youkai?
Since half youmu half humans are also called hanyou, I'm assuming they are.

However, if they are, then why are they called youmu instead of youkai?

Answer 1

In Kyoukai no Kanata, are youmu the same as youkai?

There is no such thing as youkai (妖怪) in the world of Kyoukai no Kanata. There are only youmu (妖夢).

Keep in mind that youkai is a very loosely-defined term in Japanese, and is generally used to refer to a rather motley collection of supernatural creatures, so it isn't even really all that meaningful to ask whether some term is "the same as" youkai.

(Aside: note that youkai and youmu share the character 妖, which means something along the lines of "strange or bizarre".)

However, if they are, then why are they called youmu instead of youkai?

This is a question of authorial intent, basically. If I had to guess, the author chose to use youmu instead of youkai in order to avoid bringing along the semantic baggage that the word youkai carries. Every Japanese person has an idea of what a youkai looks like, but youmu is an original coining, so you don't really have the same preconceptions in that case.