Gensō Suikogaiden (幻想水滸外伝) is a two volume series of visual novel spin-offs from the Suikoden series of role-playing video games. The games were only released in Japan and never translated into other languages.

Suikogaiden Volume 1: Swordsman of Harmonia (幻想水滸外伝Vol.1 ハルモニアの剣士)-(1999)
Suikogaiden Volume 2: Duel at Crystal Valley (幻想水滸外伝Vol.2 クリスタルバレーの決闘)-(2001)

The events of the game intersect with those of Suikoden II, but are more of a side story, hence the name gaiden(外伝) .

Source:Wikipedia