Well there is a James brown singer but he wasnt brazilian. Also, the song doesnt exist, maybe duo to copyright issues. But it may be heavily based on Garota do Ipanema.
Wich is this one:
https://youtu.be/WuenyQ4NCQE?is=OkA6l3QWHwlDvhvU
I think all of these singers mentioned in manhwa either fictional or referencing to real singer (like Zian for Zion T). Personally I think Jamie Brown was referencing to Jimmy Brown (a Korean singer and he has this angelic voice which I imagine this is what Jaeyoung's voice sounds like.) and I would imagine he was singing Sunset Glow

Genuinely asking. Is this Jamie brown singer a real person irl or is it just a character in the manhwa? Bcs i can't seem to find him or the song called sunset of ipanema by him