Masu is first encountered during Amaterasu's quests at Western Nippon, when an acrid and poisonous fog from an unknown source shrouds the entire of the capital city. The samurai is found sitting just in front of the gates to the Aristocratic Quarter, lamenting about the sickness plaguing the city, and Queen Himiko's incredible holy powers, but don't do a thing about the unnatural fog shrouding Sei'an City .
After the fog is cleared, Masu can be found in much the same spot during the day, and inside a local restaurant at night. He will mention that he has traveled to the city to slay a pack of demons. He will refuse to show the list to Amaterasu during the day, but when drunk at night he will hand it right over.
Should Amaterasu slay the demons herself, he will accuse the wolf of stealing his glory. However, if pressed he will admit that he was not looking forward to battle with the demons and is glad that the violence is over.
Not much is known about Masu's personality, but it is heavily implied that he is a serious man, as when he refuses to give Amaterasu his list of demons, and even up to the point of attacking the Sun Goddess, should she headbutts him. However, when Masu is drunk, his hangover will prompt him to do whatever that is told, and in the case of Issun's request, gives him the Monster Manifest that he normally keeps with him.
As a person of the samurai class, Masu is always seen in an attire consisting of a yellow kimono and a purple hakama, and always with him is his katana, whose sheath is made of traditional lacquered black wood, and the handle is of a slighter gray. His face is quite large, and his mustache is kept as thin strips, and he also has a small beard. As a samurai, Masu also has a flag on his back, and his hair is tied into a ponytail, with the hair on his temples pointed high.
- Masu's name is based on the Edo period Japanese naturalist Sugae Masumi (「菅江真澄」?).
- If Amaterasu headbutts Masu, he will attempt to attack her with a dashing slash, signified by his stance, his right hand on the katana's handle. The attack itself wouldn't do any damage nor costs her Godhood and can be easily evaded by any means, but should it connects, Amaterasu will be stunned for a brief moment.
- The way that Masu wields his katana may suggest that he uses the Iaido martial art in combat.
- Masu is one of the very few characters in the entire Ōkami series to have their names in the original Japanese versions written not in katakana, but entirely kanji. Naturally, this means that Masu bears some sort of cultural relevance or importance, though this is not the case for the main characters who are based on real life mythology themselves.