Pocket Jansou is a Sega Game Gear game that would likely originate from Japan given its name. Without more information about this title, further specifics concerning the gameplay, genre or setting are unknown.   The 'Pocket' prefix often implies a portable adaptation or smaller scale version of a game. Sega would have published the game.

Pocket Jansou (Japan)

Phantasy Star Gaiden (Japan) [En by Magic Destiny v1.012] (Wide Font)