Function of なワケ of 一体何の用なワケ?


> すると、士道が話を切り出すより早く、焦れたように三人が声を発してきた。 「……で、一体何の用 **なワケ** ？こんな手紙で呼び出すなんて」

Context: In the name of 士道, a letter was sent to 亜衣, one of 士道’s classmates,
telling her (亜衣) to go alone to meet 士道 in a cafe. But it turned out that 亜衣
went there in company with her friends. One of the friends questioned 士道 what
he asked them out for.

Hi. What function does the なワケ add to the sentence? It seems that 一体何の用？is
enough to express the intended meaning.

Thank you.




わけ [can mark a reason](https://japanese.stackexchange.com/a/2258/5010). If
used in a question, "～わけ?" can be used to seek a reason. In other words, the
function of わけ in this sentence is roughly the same as explanatory-の used to
seek clarification, and you probably know how important this の is in Japanese.
The sentence in question is interchangeable with "一体何の用なの?", but as compared
with の, わけ is more explicit and sometimes accusatory.




わけ [can mark a reason](https://japanese.stackexchange.com/a/2258/5010). If
used in a question, "～わけ?" can be used to seek a reason. In other words, the
function of わけ in this sentence is roughly the same as explanatory-の used to
seek clarification, and you probably know how important this の is in Japanese.
The sentence in question is interchangeable with "一体何の用なの?", but as compared
with の, わけ is more explicit and sometimes accusatory.

