ff9? dagger's song is a important plot point imo

there's a scene in umineko where jessica sings. it makes a big deal out of it and id further say why it's important but spoilers

apollo justice case 3 is extremely centred around a performance of a song, the game has this like 2 minute cutscene for it with 3d models and everything, and fans meme this case because it really expects you to watch it again and again. this game does have a bit of an overarching plot and it's not relevant to that but the character singing is important and the game only has 4 cases anyway so it's still a major part of it

...any project diva game? lol

link's awakening!

song of the ancients is a key song in nier. the characters that sing it do so multiple times, are crucial to the plot, the vocals disappear when you move away, plays in a key moment, etc

ty everyone cant believe i forgot to lead with some of those I have swiss cheese holes in my brain

In Dragon Age Inquisition, Mother Giselle starts singing The Dawn Will Come just before you reach Skyhold.

Genesis Noir also has a cool scene near the end that my game keeps crashing after :(

Might as well add Portal 2 as well.

yakuza 5

Pyre!
During the Liberation Rites the Lone Mistrel and Celeste (the girl) sing this song https://www.youtube.com/watch?v=T1k5SCCN1sk

I figured since Transistor is on here you already considered them but yeah really all of the four Supergiant games lol

If Mordin counts, would we count Majora's Mask with its musical instruments, or does it have to be a vocal track? Similar, DCMC in Mother 3 is a band with an important plot point, play multiple concerns in the game, and it's got some importance to it.

Melody in Luigi's Mansion battles you using magical music and music sheets and knowing what game the song she plays is from is required to access the boss battle. (And unlike the earlier examples, is actually girl)

Amadeus Wolfgeist in Luigi's Mansion 3 plays the background music for his first two phases which is used for his magic, complete with his attacks being synchronized to it.

Queen Mary's song and the Eight Melodies are important to Earthbound Beginnings / Mother 1, diagetically sung at multiple points and singing it is required to beat the game.

Song of Memories is about idols fighting monsters in the apocalypse with their music

The Caligula Effect/The Caligula Effect Overdose are about a Vocaloid whose music becomes so powerful that it draws desperate souls into an alternate reality, and follows their attempt to escape

How about Lephise and the Song of Rebirth from the original Klonoa? It's a really big deal in the ending.