Riba

Riba (リバ) is a term used both in LGBTQ culture as well as Yaoi (Boys Love) and Yuri (Girls' Love) fiction that refers to characters being versatile (adaptable or reversible) in the type of dominant or submissive role they can adopt.

Used in a yaoi pairing refering to one whom contains mixed traits of a seme and uke

Origin of Riba リバ
The word riba is probably just the abbreviation of the katakanization of the word "reversible," ribaashiburu (リバーシブル) or something like that.