Princess Lucia

Princess Lucia (プリンセスルシア, Purinsesu Rushia) is a manga series written and illustrated by Kōji Seo.

Plot
Koizumi Yuta is a 14-years-old boy who has quite a bit of a problem. The princess of the magical world, Lucia, has to procreate with him. That child would have the ability to engulf the entire world for 7 whole days. Mikamoto El and Kasukabe Rie are the two angels assigned to make sure that doesn't happen. Kasukabe Rie happens to be the girl he likes. Just how is he going to survive this ordeal?