Natural 2: Duo
Genres: Hentai
Type: OVA, Episodes: 4
Aired: Nov 25, 2001 to Jul 24, 2003
Studio: Arms
Source: Visual novel
Rating: Rx - Hentai
Synopsis:
Chisato and Kuu lost their parents years ago and were taken in by an Old man and his grandson, Chisato and Kuu became good friends with his grandson however he left and never came back. Now. Years later Chisato met up with her "Onii-chan" her lost love.

(Source: ANN)