Last week, Zepy of Canned Dogs uncovered the reason that Vanillaware, best known for sidescrolling RPGs like Odin Sphere and Princess Crown would veer off into a game about little girls with animal ears, and it's pretty interesting. One of their staff artists makes amateur doujin games, like Habanero-tan House (which looks like Kumatanchi with plant-girls), in his spare time with a group called Ashinaga Ojisan. Somehow, Vanillaware decided to work with the group on a DS game.
It's not uncommon for an amateur-made game to become a console release -- Melty Blood comes to mind, as does ABA Games' TUMIKI Fighters. But since this is being done professionally in collaboration with Vanillaware, Kumatanchi isn't exactly a doujin game.