While normally just used to indicate the reading of a particular kanji, furigana can also be used for certain Shenanigans.
With furigana, a word's pronunciation can be totally decoupled from the characters used to write it, and you get a hypertextual sort of additional layer of information. When you write one word and then read it as a totally different word, it's a bit like both words are being used at once. This is sometimes even applied to words that are already written in kana and should therefore already have a single, unambiguous pronunciation.
Alison Airlines' "MOCOHUASCA" (pool #14779) goes absolutely ham with all this:
- On page 3 (post #3441417), Marisa says「『アヤワスカ(これ)』はかなり強烈」– "Ayahuasca (this) is really strong stuff." In this case, we have a pronoun applied as furigana to the name of the pronoun's referent for the sake of disambiguity.
- On page 4 (post #3441419), Marisa says「私は魔女(プロ)」– "I'm a witch (professional)," saying two words at once to communicate something like, "As a witch, I'm an expert on this sort of thing"—all in the space of a single word.
- On page 8 (post #3441431), Mokou thinks「混沌(カオス)」, pronouncing (subvocalizing?) the Japanese kanji word for chaos as the Western loanword kaosu.
- On page 9 (post #3441432), Mokou thinks「『深(イキ)』すぎてる」, simultaneously saying "I went too far" and "this is too intense". A sentence later she says, 「この『領域(レベル)』」– "this place (level)", referring to her psychedelic experience as a "place" while still acknowledging it as an altered state of consciousness.
- On page 13 (post #3441441), the narrator says「舞踊(ダンス)」and「交響曲(シンフォニー)」, using the Japanese kanji words for "dance" and "symphony" and pronouncing them as dansu and shinfonii.
- On page 17 (post #3441447), Mokou says「空(すべてはひとつ)だ」– "Nothingness (all is one)." Almost the entire sentence is compressed into a single kanji.
- And on page 21 (post #3441454), she mentions「138億年も続く宇宙の輪廻(ダンス)」– "The 138-year samsara (dance) of the cosmos," using substituting in the same loanword the narration did before, but this time applying it to a very different Japanese word.
We don't have many tags relating to the text on images, but I think this might be an interesting one. We can start by going through the furigana tag and looking for examples—it's likely that a good portion of that tag qualifies, since manga that are meant to be read by people with adult-level literacy usually don't have that much regular pronunciation-aid furigana to begin with.
Updated by Lefkadios