Confusion regarding writing a word in Kanji and Katakana

Question

In the One Piece manga, it's quite common to see the names of character's attacks written in both Kanji and Katakana. Take as examples:

Gekko Moriah's Doppelman [影法師]{ドッペルマン} Dopperuman, literally meaning "Silhouette"
Daz Bones' Spider [斬人]{スパイダー} Supaidā, literally meaning "Beheading/Cutting Man"

My question is: can those kanji really work together to be pronounced like that, and the katakana is just there so people won't think it's pronounced some other way? Or is it that the kana actually DEFINES how the word is supposed to be pronounced, and I could in theory take any pair of kanji and katakana and say "you write it just like that other word, but this is a different word and here's how it's supposed to be pronounced"?

I used to think it was just clever wordplay, but there's some things that just sound too good to be true.

Answer 1

In most cases, the kanji can't be pronounced that way, as in that pronunciation does not match the standard on-yomi or kun-yomi for the characters at all. Basically, the kanji provide the meaning and the katakana show how the author wants it to be pronounced. It's a stylistic choice.

This can be seen in song lyrics, too, where a word will have kanji but it will be pronounced with its English meaning, for example 道{ロード}, or with the pronunciation of another Japanese word that is usually written differently, like 永遠{とわ}, 仲間{きみ}, or 現実{いま}.