Dengeki Daisy Manga

From Viz: After orphan Teru Kurebayashi loses her beloved older brother, she finds solace in the messages she exchanges with Daisy, an enigmatic figure who can only be reached through the cell phone her brother left her. Meanwhile, Teru meets and forms a strange friendship with mysterious Tasuku Kurosaki, her school's janitor. For some reason, Kurosaki always seems to be around whenever Teru needs help which leads Teru to wonder: Could Daisy be a lot closer than she thinks? As the mystery of Daisy unfolds, Teru also discovers that there may have been a lot more to the life and death of her brother than she ever dreamed . . . and that the man she thought was her friend just might have all the answers.