From MangaHelpers:

Minaguchi Kaoru is nothing special. He's no good at sports or school, isn't in any clubs, and he's not popular. He has no friends and isn't even interested in any of the girls he knows. He's also teased due to the fact that he loves shoujo manga. Unlike the harem daydreams of his peers, he dreams of finding his true love. Unfortunately, a shinigami comes to kill him, simply because he's a "forever alone" sort of guy. When he gasps out his intention of embracing life with his final breaths, though, she takes it back! As long as he follows through on his intentions, he won't be killed.

To convince the shinigami that his plans are genuine, he declares that he will confess to the girl he likes, the very next day. Expecting failure with confessing to random girls in his school, he sends out love letters to four different girls. To his surprise, they all agree to be his girlfriend. Now, this shoujo-manga-loving guy has ended up in a kind of harem story, quadruple-timing four girls! Will he be able to stay involved enough with society to avoid an early death? [tethysdust]