Post game characters singing here.
To start off, I’ve grabbed a few games, categorized in various ways.
We have player characters singing, decided by whether they’re singing Karaoke of not.
Karaoke:
Not Karaoke:
https://youtu.be/QuqMbCCUclQ">https://youtu.be/QuqMbCCUclQ
Then we have various party members singing:
Non-party member characters:
And then all of the above:
Both of the Dominique Pamplemousse games are musicals where most dialogue is sung!
@“Funbil”#p100122 Yes! How did I forget about DomPam?
I assume Parappa and other characters from pure musical games are out of this specific conversation.
I won’t post it in too much detail since it’s a memorable moment one can experience in a relatively recent game but that moment in Elden Ring (typically near the Weeping Peninsula) when you hear somebody singing for the first time, and try to find where the singing comes from, comes to mind. Pretty clever use of a diegetic song inside a video game.
Another iconic “diegetic singing” moment from this generation: Mayor Pauline singing during the New Donk City festival in Super Mario Odyssey. I have questions regarding the proper use of taxpayer money for re-election campaign purposes in New Donk City.
Speaking of Mario songs, there was also this hommage to @“airconditioner”#p100121 Conker’s Bad Fur Day’s Great Mighty Poo in Mario+Rabbids: Kingdom Battle.
Also, SNK girls singing!
★KOF’95 Neo Geo CD special ending
★Real Bout Special Neo Geo CD special ending
Parasite Eve starts with an opera scene.
A character in Disaster Report 3 sings at least twice in the game. On mobile I can't copy link at the correct time so scrub on over to 1 hour 20 to enjoy.
Deadly Premonition
Incidentally "it's too late to love you now" is what I said to episodes 4 and 5 after the long wait for their release rofl
I can think of a few games where characters have sung a song in the game‘s lore, like how Julia is the singer of “Eyes on Me” in FFVIII’s world or how Red sang “The Spine” in Transistor. There's also non-lexical vocable performances like this one
Also sorry it's only fair to include the superior Polish version of “Wilcza Zamieć” (whose literal translation “Wolf Blizzard” is so much funnier than the official localized title lol) as well:
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@“connrrr”#p100156 non-lexical vocable performances
just quoting those words 'cuz i like 'em so much
Last one: for my buddy @“DavidNoo”#503
(4:44:30 to 4:47:25)
I guess I have to be the one to post Idolmaster
@“connrrr”#p100175 so good! Thanks for sharing 
Randomly thought about Matrimelee, so how about entire fighting game backgrounds singing for you?
That Internet song (1m45s) was quite popular in its day on message boards like the Madman’s Café.