Teizokurei Monophobia

Houdzuki Maika is a high-school girl who, in a sense, is never alone. Her twin brother Maito, who could not survive birth, lives inside of her and shares her body. They switch between who gets to live each day and they 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 share the same dream. Perhaps as a result of this supernatural existence, they are able to see ghosts. There will surely be many mysterious incidents ahead for these twins to face! (Source: Mangamonster.net)