What is the connotation of まぐわう (referring to intercourse)?

Question

I understand that まぐわう essentially refers to the act of sex. But I'm trying to get some idea of the connotation. In Yofukashi no Uta, it's translated/localized as "copulate", which has a very scientific connotation in English, as well as the connotation of producing offspring being the ultimate goal. It's also rarely applied to humans in any normal conversation. Is that roughly on point?

To contrast with this: to my knowledge, エッチ, だく, and セックス are much more "commonly" used with a personable connotation, and やる being used more akin to "fuck"'s connotation in English.

Sorry if such "nsfw" questions aren't allowed here @.@.

If it provides some context: a pretty vampire japanese nee-san was referring to sex between humans with まぐわう, and a 14-yo boy was getting flustered by the usage of that term, asking why she insisted on using it in particular.

Answer 1

Note that there is no entry for まぐわう in most dictionaries (including 大辞泉). There is only 目合ひ(まぐわひ), which sources Kojiki, the oldest text in Japanese.

まぐわう should be a verb made from まぐわひ, most probably so as to give pseudo archaic effect in fictional texts. In other words it is almost never used in real life (except perhaps half-jokingly among people who love fictions). As such, it sounds literary and erotic without being dirty.

This may be just me, but it has some connotations of being passionate and of being entwined during the act due to the similarity to まじる/まざる.

Answer 2

まぐわう almost never appears in scientific contexts or news articles. This is a literary word, and I expect it used mainly in elevated novels. It's not used for copulation of animals and insects, either (unless joke is intended).

That is not to say adults never use it in conversations, but only someone who speaks in a mature and pompous manner would naturally use such a word. If this girl is the one who used this word, she seems to meet this condition.