Kinu Himuro
A teenaged female ghost. First encountered by Mikami and Yokoshima as one of two ghosts causing chaos at a mountain hot spring, Mikami ends up "adopting" her when she doesn't go to heaven after the end of the first mission in the manga. Eventually, she ends up becoming the secretary and errand girl for Mikami and even develops feelings for Yokoshima.
Pictures
Mangaography