Teizokurei Monophobia

Houdzuki Maika is a high school girl who, in a sense, is never alone. Her twin brother Maito, who died before their birth, lives inside her and shares her life. They trade off on who gets to live each day and share most of their memories. However, the only times they get to see and talk to each other is when they are both asleep, where they can share the same dream. Perhaps as a result of this supernatural existence, Maika is able to see ghosts. In the first volume, the school counselor pulls Maika/Maito into helping out with discovering the truth behind the disappearance of a female student whose ghost has left a message scratched into their classmate. There are surely many more mysterious incidents ahead for the twins to face!
(Source: MU)