Jun Onose (小野瀬潤, Onose Jun, born on August 12, 1970, in Hadano, Kanagawa), better known by his stage name J, is a Japanese musician, singer-songwriter and record producer. He is best known as bassist and co-founder of the rock band Luna Sea since 1986. After they disbanded in 2000 he focused on his solo career, for which he performs lead vocals and bass. He rejoined Luna Sea when they reunited in August 2010.

Since 1997, J has had prominent names in the music industry playing either on his albums, as his backing band, or showing up as guests at some of his concerts including Raymond Watts (PIG), Ray McVeigh (Zilch), Takashi Fujita (Doom), Scott Garrett, Billy Duffy and Ian Astbury (all three from The Cult), Steve Jones (The Sex Pistols), Duff McKagan and Slash (both from Velvet Revolver), Franz Stahl (Scream, Foo Fighters) and Youjeen (Cherry Filter).