When Shiro’s mischievous sisters, Shiori and Saori, come to stay with him, it is perhaps only a matter of time until they stumble upon the portal to another world. And so, when the inevitable happens, Shiro accompanies the twins on a stroll through the forest just outside of his usual stomping ground, Ninoritch. The wide-eyed high school girls are captivated by their otherworldly surroundings, and when they find an enormous egg, they are determined to take it with them and find out what’s inside. A quick trip to the Adventurers’ Guild sees the egg identified as one laid by an ebirasornis, a giant birdlike creature that can be used as a mount, and at this news, the twins exclaim they will raise it themselves. But is there really an oversized chick inside this enormous egg? Meanwhile, Shiro bumps into a mysterious woman who appears to have lost something very important. But what could it be? And who is this laconic stranger with a strangely menacing aura?