Muta

Muta, also known as Renaldo Moon, is a supporting character in The Cat Returns.

Personality
Brash and grumpy, Muta is known for his unchecked sense of sarcasm and condescension towards people and his other companions, and for his huge appetite. This accounted for his chagrined relationship with Toto, whom he has a mutual dislike with, though they wouldn't hesitate to team up and work together when the need arises. In spite of his seeming indifference, he did eventually warm up to Haru, whom he praised for standing up for herself and later aided in her escape from the Cat Realm.

Ability
Similar to the inhabitants of the Cat Kingdom, Muta can walk bipedal, speak human speech, and perform human-like deeds.

Most notably, Muta is confirmed to be alive for many years where his unusual longevity is a mystery according to Cat King.

When Muta described about the Cat Kingdom, he said "that place is a bamboozlement where ones, who cannot live in their own times like me, go". Additionally, Cat Kingdom is confirmed to be an afterlife for cats who died in living world in the book. As Muta traveled between living world and Cat Kingdom on at least two occasions, it is implied that he is either a magic user or a supernatural being, being a spirit or a half-dead with either an extremely long life span or immortality. This is also somewhat consistent with the fact that he befriends with Baron and Toto, artificial statues that gained souls.

In the book, it is also revealed that Muta can pronounce Yu (ゆ) sound where cats usually cannot pronounce. Muta achieved this due to his long life experiences. The Baron can also pronounce the Yu sound because he is an artificial being. Yuki can also pronounce the sound possibly due to her status as a dead spirit.

Cat Baron
Muta and Humbert von Gikkingen are the main protagonists in the series.

Whisper of the Heart
Although the character design is very similar, in Whisper of the Heart Muta is known mostly as "Moon" by Shizuku and Seiji, and is only called "Muta" once at the end of the film by an unnamed girl who seems to be one of Muta's owners. Much like in The Cat Returns, Muta's purpose in this film is to lead the main character, Shizuku, to the characters who will help her overcome her challenges and grow as a person (these characters being Seiji and his grandfather, Mr. Shirō Nishi).

Although The Baron is introduced in this movie and plays a pivotal role in both the lives of Mr. Nishi and Shizuku, his role is a symbolic one, as he remains an inanimate object throughout the film, only coming to life in Shizuku's book. Muta, as he is depicted as a more average cat, doesn't appear have any connection to the Baron in this film/doesn't acknowledge him.

Whisper of the Heart: Happy Time
In the sequel to the original Whisper of the Heart manga, Muta is the chief of the Cat Library. When Shizuku Tsukishima wandered there, he initially refused her.

The Cat Returns
Muta was given a supporting role in The Cat Returns, where he is depicted as the Baron's portly companion at the Cat Bureau. A mysterious voice instructed Haru to look for Muta at the Crossroad where he frequents, who leads her to the Bureau to meet the Baron. Soon after meeting them, Haru and Muta are forcefully taken to the Cat Kingdom, leading Toto and the Baron to go after them.

Inside the castle, Haru and Muta are treated to a royal banquet, but Muta is suddenly trapped in a pitcher of catnip jelly; he eventually escaped in the ensuing fight when the mysterious visitor who danced with Haru is revealed to be the Baron himself. He, Haru and the Baron were then aided by Yuki, a servant cat who initially warned Haru to leave the Cat Kingdom.

As they were confronted by the King, Muta reveals that he is actually Renaldo Moon, a notorious criminal who gained a reputation for devouring a whole lake of fish at one time. Muta praises Haru for standing up for herself after rejecting the King's proposal to marry him, and helps the Baron and Haru escape from the cat realm.

Yume no Machi: Neko no Danshaku
Muta appears as a stray cat who lives nearby Aki's house in Aoi Hiragi's manga spin-off of Whisper of the Heart. He is interested in the statue of The Baron.

Trivia

 * Unlike in the film, Muta was described to be a black and slender cat in the books.
 * He and Moon and Niya from The Secret World of Arrietty were modeled after Ushiko (牛子, lit. "Cow Girl/Child"), a pet cat owned by Studio Ghibli.
 * His name and wrestling scene were based on Keiji Muto who is commonly known as The Great Muta.
 * Muta / Moon and Humbert von Gikkingen are the most recurring characters in Ghibli works as appearing in five different works, followed by Minonohashi that have appeared in four different works.