Senyuu.

Once upon a time, a Demon King named Rchimedes caused havoc and destruction in the Human World. He was sealed away by the great hero Creasion, and peace returned to the world.
1000 years later, Rchimedes has returned, a hole has opened up in the Human World and countless monsters have sprung up. To prevent any further destruction, the King calls upon all 75 (probable) descendants of Creasion.
This story focuses on the adventures of descendant number 45, Alba, and the royal solider appointed to assist him, Ross.