One of my favorite parts about Splatoon is the music. Splatoon does something really interesting with their music that I don't think any other game has done.
Every single song in Splatoon is heard in-universe by the NPCs, that's because every single game you hear (in the menus, during matches, in shops, in maps) are all "produced" by in-universe bands and artists with their own members, designs, backstories, genres, and albums.
Even the instrumental music that plays in the singleplayer campaign is canonically a real album called "Turquoise October" which was produced by the octarians.
From rock, to pop, to metal, to rap, hip hop, orchestral, dubstep, synthwave, techno, chiptune, reggae, jazz, or even celtic rock, all of the genres are represented by a fictional band or artist in the world of Splatoon.
Most of the singing done are literally done by members of these in-universe bands, each with their own singer to represent them. It's basically just a self insert of the composers haha
(if you want to learn more about the music of Splatoon, here's a very good video)
If you've played Splatoon though, you'll know that the characters don't actually speak english or japanese or any real world languages. They speak a variety of fictional languages, but since you play as an inkling, you're most used to seeing shops written in the inkling language.
Songs are also sung in the inkling language.
Similar to "Simlish" from The Sims, the inkling language isn't actually translatable and is entirely gibberish.
However, some more important words (such as certain signs, or important lyrics in songs) barely mimic real english or japanese words.
It's not uncommon for fans of Splatoon to write their own lyrics for the songs, since some gibberish does almost create the illusion of hearing real words.
This section will be a place for me to share the lyrics I've personally came up with for some of my favorite Splatoon songs.
Please note that I try my best to have the lyrics make sense given the context of the song, actually sound like the lyrics, keep a consitant theme, and not sound too cheesy!