Mamoru has short neat black hair and deep blue eyes. He is usually seen wearing his school uniform; Dark blue jacket over a white dress shirt and a red neck tie, long grey dress pants, and black shoes. He wears glasses when reading.
Act 1 - When Usagi is upset about her grade on her latest test, she crumbles up the paper and throws it behind her, hitting a Mamoru who is dressed in a tuxedo. He complains to her, while making fun of her hairstyle and calling her "Bump-head". Usagi begins to complain to him, "they're buns not bumps". Mamoru begins to call Usagi "bun-head". When their eyes meet, they suddenly stare at each other in awe and Usagi's heart begins to beat faster. Mamoru stands outside the jewellery store, wondering if it might have the Legendary Silver Crystal he is seeking.
Act 2 - A teacher from Crystal Seminar hands a flyer to Mamoru. Usagi who also received a flyer, crumbles hers up and throws it behind her hitting him in the face. Mamoru questions Usagi when he overhears her cat talking to her, which Usagi immediately declines.
Act 3 - He is sitting next to Usagi at the back of a bus, he shows her his student ID card introducing himself as Mamoru Chiba a second year student at Moto-Azabu Private High School.
Act 4 - While looking for her handkerchief to wipe up Usagi accidentally drops it without noticing and Mamoru picks it up.
While Usagi is sitting outside of Princess D's ball alone Mamoru, who is unrecognised as Mamoru and believed to be Tuxedo Mask by Usagi because he is wearing a mask, asks Usagi to dance. They go inside and dance together.
Act 6 - When Usagi wakes up in a strange apartment, she discovers Mamoru is the true identity of Tuxedo Mask.
Act 7 - While in Mamoru's apartment Usagi spots Tuxedo Mask's Top Hat and Mask. Mamoru describe that Usagi blacked out after her last battle and has been in a deep sleep ever since. He explains he became Tuxedo Mask in the first place to regain his lost memories and he needs the Silver Crystal to get them back. Usagi listens as Mamoru reveals that his parents were killed in a car crash on his sixth birthday and it was a miracle he survived but with no memory. After having a recurring dream filled with one phrase "Find the legendary Silver Crystal" he found himself roaming the streets at night, searching for the Silver Crystal in hopes that it was a clue to his lost memories. He wants to keep everything a secret between the two of them and he calls Usagi, Usako. Once Usagi leaves Mamoru's apartment she decides to call him Mamo.