I need to find a seinen manga?

[DarrisonSaber]

So this manga was a manga i read a few years ago and i want to go back to reading it, but i forgot the name. It's a about a boy, somehow the rest of the world is asleep, and this is what i know so far. The cover is probably blue and i think it has a lady on front. The genre is ecchi, seinen and maybe sci-fi? Plz help me!
and oh yeah, i think it's completed already.