I had a request to add the original Monster RPG game, which was called "Monster" (labelled as Monster RPG 1 now to avoid confusion... although it may just create even more...) as a DLC and it is now live:
http://store.steampowered.com/app/420240
It's free for Monster RPG 2 owners. The game is a little rough around the edges and does not contain great graphics (all made by me, not an artist) and the gameplay is extremely grindy. You do not need to play it as Monster RPG 2's story is not connected in any way to the first part. It is added as a convenience to Steam users who may like to have the complete series in their Steam collection.
Enjoy.