OP: Inferno from Fire Force
ED: Torches from Vinland Saga

I've had genuine thoughts about this before, the only ones that hang around consistently are these two's
Silvana: OP - [Konoyo Loading - REOL] | ED - [Virtual - Moe Shop]
Linnaea: OP [The Beginning - ONE OK ROCK] | ED: [American Girls - ONE OK ROCK]

In regards to Odd:

For the Ed, I'll be a normie and say The Real Folk Blues from Cowboy Bebop; the bluesy vibes would fit well for him, I'd think.

As for the OP, I'll stray into possibly cringey AMV territory and forgo an actual anime track entirely: No Surprises by Radiohead. Can't help but think of that song a lot when relating to Odd.

Eve is far too predictable since they're both Pokémon. Buy Pokémon songs just fit her best lol

OP would probably be XYZ
ED would be Type:Wild

Right now I only have EDs in mind for my characters, but...
Ming-Ming - Don't Walk Away by Jade
Kazuki - Another Star by Stevie Wonder

That's a tough one, but if I had to pick two songs, I say something high best like Sonic Frontiers' Undefeatable, and for the ending, something like The Case Study of Vanitas's season 1 ending

ACTUALLY I HAVE an entire soundtrack for Mariah’s story AHKDJD but i will just leave one op and one ed hehe

OP song: My Foolish Heart (Crazy on Earth) by Soil & Pimp Sessions https://youtu.be/Hn6JHXyjOEU

ED song: Waltz ga Kikoete by Quasimode https://youtu.be/RiZM_upap0w

Honestly-speaking, never thought about it that much. But if I have to throw out an OP and ED example that would work in Elio's case:

[Two Divided Rainbow] by STEREO DIVE FOUNDATION (Opening)

[Loser] by Kenshi Yonezu (Ending)