La.Moo

Main character goes to an archaeological site during his last high school summer and gets into a different world. It's an ancient city Moo on the territory of the sunken continent that disappeared 12,000 years ago. There he meets three sisters and starts to live with them. However, the Moo Imperial government makes a move as soon as it learns about protagonist's origin as the man from future. He gets an invitation from God's representative La Moo. What's the truth about Moo continent disappearance?