Euria Sin, better known as OR3O (often stylized as OR3O★), is a Korean-American musician. She is known for making original songs, covers, and remixes about video games, movies, and TV shows, making her a pioneer in the nerdcore genre. She has often collaborated with other nerdcore musicians and groups such as CG5, Random Encounters, and The Living Tombstone.

OR3O started uploading her songs on her YouTube channel on July 13, 2015. Her first song, a cover of “Unravel” by TK from Ling tosite sigure, was uploaded one day later. In the YouTube video’s description, she revealed that she uploaded (and re-uploaded) this cover for fun:

I actually posted another one before this but i reuploaded this one because the other one was deleted by copyright. But I uploaded this so show to my friends and I did not expect this to get any attention at all (honestly im just extremely lucky lmao). I hate this video because its terrible but I love it because it brought me to where I am today (even though i didn’t post for a year after this).

Three years later, she remade the cover with help from RichaadEB as a throwback to the first cover.

Original concepts appearing in OR3O’s discography include her debut album, Clover, which is full of electro-swing music. It focuses on the main protagonist named Kelsey “Kel” Clover, who aspires to be a music producer but is ridden with unlucky events, such as depression and her grandfather, who believed in her dream, passing away.

OR3O is the founder of the band ROYALE5, which was created to be both a VTuber project and an entry to Vintage Choir Battle 2023 (VCB 2023 for short).