Title: Tokidamari no Hime, ときだまりの姫
Author: Shinohara Chie
Genre: Josei Romance Supernatural
Length: 2 volumes (complete)
Story about a mirror princess/demon. It seems that a new condo building was built on a certain location where this princess was housed and worshiped with a stone monument but it was moved due to the new construction.
One room in particular seems to have a direct link to the princess who calls herself the owner of the pool of time. Beware when mirrors are placed opposite of each other because you may just be drawn in her world and powers.