I'm reading a short story called "The Iceman" (my translation for 氷男). The book is a "real" book (i.e., not a simpled-down book for people learning Japanese) that is meant for native Japanese readers.

In the book the kanji are glossed with the furigana "koori otoko".

I'm curious as to why, because I knew right off the bat to read the characters as "koori otoko" and I'm still just learning Japanese.

Is the furigana necessary because there are other more common readings (e.g., a proper name)?

Probably to keep people from using on-yomi. You see the same things with names and other words that could be read multiple ways.

I've even seen 昨夜 with furigana in the same book with 轢かれる without. Also there's fact that I don't think that 氷男 is a established word.

I read it as ひょうなん first but thought that didn't sound appropriate for a made-up word so figured on こおりおとこ by analogy with 狼男 and 雪男. I then read the rest of your post

tetsueda Wrote:I've even seen 昨夜 with furigana in the same book with 轢かれる without.

It could be justified for 昨夜, since it has two legit readings with differing levels of formality (ゆうべ and さくや), so the author might have wanted to make sure the readers know which reading was used in that case.

Because they wanted people to know how to pronounce it. It's not at all obvious that it's こおりおとこ.

tetsueda Wrote:I've even seen 昨夜 with furigana in the same book with 轢かれる without. Also there's fact that I don't think that 氷男 is a established word.

Is that the Kanji for getting run over? Asked the roomie before, and she said she never saw it in Kanji. Dang Japanese don't know their own language.