Final Fantasy Adventure launches the Mana series in Japan
Square released Final Fantasy Adventure (Seiken Densetsu) for Game Boy in Japan on June 8, 1991 — the action-RPG that quietly started the long-running Mana series.
Source: Altered Gamer, This Month in Video Game History — June 8, 1991: Square released Final Fantasy Adventure as Seiken Densetsu: Final Fantasy Gaiden for Game Boy in Japan