Countdown 7 Days Vol.1 (2011)

Onigawara Hanasuke finally realized that he had died - when Mitamura, a dark haired guy with glasses from "another world" told him so. Hanasuke is shocked and saddened from the news, but Mitamura lets him in on a little trick - he can revive himself! Sounds like a great story, but in exchange, Mitamura asks Hanasuke to help him to find someone and he only has 7 days to do it...