There are multiple artists that go by the name oni.
1) ONI is a croatian hip-hop group. Members are Scriptor, Jantar, Kali (MC's), KolAK47 (producer) and DJ Noki Nole. Their first album titled Lajtmotiv came out in 2015.
2) Akinyeme Olagdeji Odawali Oni Orison is a rapper who made sophomoric slump with Beatmonger's productions. The two met while going to the University of Michigan.
3) A Brutal Death Metal band from Adelaide, South Australia. Read more on Last.fm