Nii-chan is Shiemi Moriyama's Familiar that she summons during the demonstration after Izumo Kamiki summoned two spirit foxes. It is a baby Greenman spirit that takes a liking to Shiemi often sitting on top of her head. Nii-chan aids Shiemi by producing plant from it's body such as aloe and sprouts tree branches as barriers. Nii-chan appears protective of Shiemi as he shields her from the falling debris during a mission in the amusement park with tree barriers. Possibly because it's still an infant, it does not think of Shiemi or the humans as a threat. It speaks by saying the phrase "Nii!"

(Source: Wikia)