Treasure Hunter Mai, a hentai RPG game developed by Doujin Circle Gyu. Released August 9, 2015. Available for download on DLsite.com for $18.00. Available for PC Windows. Partial voice acting. Free demo available.
Mai is an adventurous girl who finds a portal to a new world. The world is filled with treasure! Leonard Poire, the greatest treasure hunter to have ever lived, recently died and left behind his greatest prize.
Source: N4G PC [NSFW] Hentai Game Review: Treasure Hunter Mai – Hentai Reviews