From MangaHelpers: 1x1t5l

"Yoku" (desire) erodes humans, causes them to lose their reason and eventually become beings known as "Yokukai." They end up moving to a strange other world that is peopled by entities who have no bodies and who seek to take them from humans. When Hinagata Anzu's friend Sou collapses on the street one day, Anzu gets a glimpse into that other world. Later, to save another friend from the same fate, Anzu makes a contract with one of the other world's inhabitants. According to the contract, Anzu will eventually surrender her body. Regardless, Anzu is determined to find out what exactly happened to Sou and to save her, if it isn't too late. Her new partner has his own plans, involving opening the many locks on Pandora's box... [tethysdust]