So I decided to binge on some more Seungyoun/Luizy on SMTM5, V App, and 1theK. While I was browsing through comments, I finally put 2 and 2 together!
Luizinho was his Portuguese name when he was attending school in Brazil. He shortened it to Luizy for his Rap stage name. Jimin from 15& didn't actually help with the that name.
If you listen carefully to his parts in his collab with Flowsik, you'll hear him say "Drink Color" a couple times. Turns out he's created a legit crew by that name, consisting of Himself, Eden, Nathan, and Oddtom. They composed the song "Recipe" and they plan on putting out more tracks soon. (according to the V App broadcast on Uniq's channel on 7/29)