Mamoru is a monkey shikigami who was created by Nanami Momozono as a test from Otohiko to determine if she was prepared for the Divine Assembly in Izumo. The egg that contained Mamoru was supposed to be hatched within 7 days, but due to an argument between Nanami and Tomoe, it was accidentally stepped on and cracked by Mizuki. Despite being premature, Mamoru already had the form of a small monkey when he began to hatch. After the incident, Nanami kept Mamoru with her so that he could continue growing off of her chi. Three days after his birth, Nanami was attacked in the library by a yokai and rescued by Tomoe. As a result of being exposed to miasma, Mamoru became ill from Nanamis depleted chi. Later, Otohiko scolded Nanami for her poor responsibility as a Shikigami caster and advised her to stop mass-producing talismans and treat her shikigami as one instead. Nanami chose "protection" as the name/ability of her shikigami, which became known as Mamoru.