When can a word normally read with its on-reading be read with its kun-reading?


I've been trying to improve my Japanese by memorizing songs I like. My current
effort is 白虎野の娘 ("The Girl in Byakkoya") from the movie パプリカ.

The line at the end of the first full verse has me confused. Most sites I've
found the lyrics on have it like this:

> 高{たか}台{だい}に現{あらわ}れた 名{な}も知{し}らぬ人{ひと}は懐{なつ}かしく

...with the English translation:

> Someone whose name I don't know appeared on the high ground and its moving

("And its moving" doesn't really make sense and I don't see anything like
"moving" in that line, but anyway...)

In searching around and trying to understand this line I happened across an
alternate rendering offered by a smaller number of sources:

> 高{たか}台{だい}に現{あらわ}れた 名{な}も知{し}らぬ広{ひろ}野{の}は懐{なつ}かしく

...which one site translates:

> Then you find a nameless and nostalgic field on a hill.

Not only does that make more sense, but if I listen carefully to the singer
(for example [here](https://www.youtube.com/watch?v=yx9RgTiIKDE) around 1:02)
it sounds like ひろの, not ひと with an extended final vowel as I originally
assumed.

The problem now is that I can only find that 広野 meaning "field" or "plain"
should be read with its on-reading こうや, not its kun-reading ひろの, which only
seems to applicable to names of people or places. I couldn't find a single
source which suggested otherwise.

My best guess is that kanji can perhaps be read using whichever reading one
wants if it makes a poem or song scan better. Is that what's happening here?
If not, what's going on?

Bonus sub-question: How is it that the word for "unknown" is 知らぬ instead of
知らない? I have the impression from watching various shows that ね can be used in
place of ない at the end of a negative, but ぬ is totally new to me.




Second question first: ぬ is an archaic/literary negative form.

[What is the difference between the negative forms -ず and
-ぬ?](https://japanese.stackexchange.com/questions/235/what-is-the-difference-
between-the-negative-forms-%E3%81%9A-and-%E3%81%AC)

It's very common in song lyrics.

As for 広野:

<https://dictionary.goo.ne.jp/jn/188918/meaning/m0u/%E5%BA%83%E9%87%8E/>

It's certainly not out of the question to read a word in an unusual way in
lyrics for poetic effect/meter/just because, but in this case the word can be
pronounced either way.




Second question first: ぬ is an archaic/literary negative form.

[What is the difference between the negative forms -ず and
-ぬ?](https://japanese.stackexchange.com/questions/235/what-is-the-difference-
between-the-negative-forms-%E3%81%9A-and-%E3%81%AC)

It's very common in song lyrics.

As for 広野:

<https://dictionary.goo.ne.jp/jn/188918/meaning/m0u/%E5%BA%83%E9%87%8E/>

It's certainly not out of the question to read a word in an unusual way in
lyrics for poetic effect/meter/just because, but in this case the word can be
pronounced either way.

