Zetsumetsu King -Seikimatsu Inran Kyousoukyoku-

Main character calls himself the Extinct King. (Zetsumetsu King) Who has the power to destroy all life on Earth. He sets an aim to have sex with seven women in the span of a month. But alas, he does not have the power to control the will of the girls, so he starts with nanpa.

[From vndbreview]