Ghost_Talker's_Monophobia Vulgar_Monophobia
A supernatural manga series written by the same writer as teizokurei_daydream, with the same artist as mahou_shoujo_tokushusen_asuka, and set in the same univere as Teizokurei Daydream.
The story's heroine, Maika Houdzuki, can see and interact with ghosts, but more significantly shares a body with her twin brother Maito. When Maito struggled to survive in the womb, Maika absorbed his spirit, and now they take turns controlling her body. 
The twins are coerced into helping to deal with various supernatural problems.
teizokurei monophobia