Angel Sanctuary, Volume 5 — Kaori Yuki

Setsuna has seven days to find his beloved sister Sara in the afterlife, and the first stop is to find the Guardian of the Hellgate--a being any normal person would avoid! Kato, an old enemy of Setsuna's, is now his only companion, but Kato has a history of being manipulated in life. Now that he's dead at the hands of Setsuna himself, just how far can he be trusted?