Definition - What does Hitachi Harness mean?
A Hitachi harness is any harness one might use to attach a large, wand style vibrator such as the Original Magic Wand (frequently referred to as the "Hitachi") to a partner for hands-free use. Rope harnesses are particularly popular for this use.
Kinkly explains Hitachi Harness
Hitachi harnesses are popular in BDSM play where a dominant partner might use one on a submissive partner for forced orgasm play. Because of the strength of the Hitachi, it can be overwhelming for many users, attaching it so that it cannot be removed from the genitals can create an extremely intense experience. This type of scene should always be clearly negotiated beforehand.