Momoiro Guardian

About
Momoiro Guardian is a visual novel released in 2009 by Alice Soft. Game genre is described as "Mote Mote Demon King Deadly Etchi ADV". It takes place in a world similiar to ours, Japan. This game is rather lighthearted being school life/comedy/romance with only happy endings. There are 4 main heroines, every with one's route.

Background Story
Seno Takuma is relatively normal student. He lives with his mother in a house that is adjacent to his family's martial arts dojo. One day his mother tells him that he will become Demon King on his next birthday, since his grandfather was also demon king (and Takuma will have his birthday in 12 days). As it is the first time he heard anything about things like demon kings being real, he is reluctant to believe that story but soon after he is attacked by girl, Rena Furourein, that claims to be the hero that will slain him. He is saved by another girl, Kirisaki Kaede, that claims to be from Demon Sword clan that protects Demon King. The girls eventually enrolls to his school and starts living with him to observe (hero) and defend him (demon sword) more effectively. Later they are attacked by Evil Organisation - that wants Demon King to awaken and The Church that wants to slain Demon King.