I'm pretty sure you have to go to twitter and then go click towards enty.. and then buy/support the game which is around 500 yen. Its a shame that it is not on dlsite, as an American.
Maybe I'm dumb, but I can't figure out how to buy anything on enty. They use a point system on the site and when I follow links to the point purchase page I get this blank page that doesn't have any buttons or obvious links.