The protagonist of our story, Moriuji Haru, is just about to complete an unnamed RPG, but just as the final boss is in his death throes, the game's heroines appear in his room!
They say they have escaped the game world and come to the real world in pursuit of the Demon Lord himself.
Haru is understandably shocked by this sudden, unbelievable turn of events, but the girls are overjoyed that they can finally meet the 'Hero of Legend' who is so famous in their world.
When the girls reveal that they can't remain in the real world without having sex with him, Haru succumbs to their pleas, and so begins the story as he tries to help in the search for the Demon Lord while educating the ignorant game girls in the ways of lovemaking...

[From MangaGamer]