Seiin no Meikyuu

Cremar Kingdom. There are many ruins of prehistoric civilizations that provide treasures for the government. Therefore, the kingdom has a school for adventurers. One particularly successful adventurer found a “forgotten god” at an archaeological site - it was a dark god of "sleepless recklessness". For satisfying his sleep desires god promises huge power. The finder becomes an instructor in the Royal Adventurer School of Cremar only to lure girls into a trap for the god...

[From vndbreview]