His main appearance is that of a tiny monkey with brown fur and eyes and a red apron. Due to his small/premature size, when Mamoru occasionally changes into his human form, he looks like a small child. When in this form, Mamoru has pale skin, and his usual brown eyes and hair. His red apron remains, except it now has his name (護) written on the front in black.
Mamoru has a very affectionate personality, but also a very cheeky side.
Mamoru tends to stay very close to Nanami, mostly sleeping in her bag, her clothes, or resting on her head/shoulders. He is very eager to help her, and alerts her of oncoming dangers that are nearby. He is very affectionate towards her, and is able to synchronize with her in order to purify evil spirits.
Mamoru does not like Tomoe very much due to the fact that Tomoe always degrades him about his size and usefulness. He often does what he can to annoy Tomoe and has been known to scratch at him whenever Tomoe upsets him.
Mamoru and Mizuki seem to have a good relationship, as seen when he and Mizuki reacted in unison when they were separated from Nanami on the way to the Divine Assembly.
Mamoru and Otohiko also seem to have a good relationship as seen in the nurse's office when Otihoko was petting him and giving him a banana.
- Mamoru's name "護" means "to protect", which Nanami chose in order to give him a purpose as a Shikigami.
- Tomoe suspects Otohiko had something to do with Mamoru having a form even though he hatched 6 days early.