- "Because I know that whatever happens to him, he'll learn from it. Also, I smoked a joint before we came."
- ―Rosa to Carmen Diaz[src]
Rosa was born on May 19th, 1958. After her daughter Carmen learned that her husband was not who she thought he was, Rosa fled Ecuador with her daughter and unborn grandson, and constantly moved around the United States, most recently from Riverside.
Rosa is first seen in the third episode of Cobra Kai, Esqueleto, where she assumes Miguel is jacking off after hearing him grunt while training in his bedroom. She asks Miguel what costume he wants to wear for the Halloween dance and he says that he wants to go as Deadpool. However, Carmen is unable to afford the price of the costume so she says that she can make him one. She inquires about his injured hand, but her Rosa brushes off her concern.
Carmen later forbids Miguel from training and argues with Rosa about the training, in which the younger woman calls Johnny a "bad influence" and a "loser".
Carmen and Rosa are later seen attending the All-Valley Karate Tournament, rooting for Miguel. Carmen is concerned when Rosa seems too relaxed about Miguel's injuries. Rosa claims that she smoked a joint before they arrived.
In the season's ninth episode, "Pulpo", Carmen is seen getting ready for her date with Johnny. Rosa tells Carmen that she is "hot for teacher" (a reference to the 1980s Van Halen song of the same name) and tells Johnny not to "knock her up". Carmen is embarrassed by this, whereas Johnny, who speaks no Spanish, simply nods politely (likely thinking she is wishing them a good evening). In the season finale, "No Mercy", Rosa is later seen at the hospital. Carmen angrily lashes out at Johnny, accusing him of what happened to Miguel. While Rosa is also appalled by her grandson's condition, she does restrain her daughter from further anger against Johnny (not wanting her to say something she'll regret), at least accepting his apology and not considering him responsible for Miguel's hospitalization.
Rosa only appears in two scenes at the hospital when she is with Carmen, both saying they love Miguel and hope for him to come home in Season 3, Episode 1 in 'Aftermath'. She appears in another scene on Miguel's surgery turnout and begs Johnny to save Miguel and help him walk again which he does. Rosa is very happy along with Carmen that Miguel is walking again and seem to have both thank Johnny for everything. Rosa is proud of her daughter's (Carmen's) relationship with Johnny.
In the first episode, Rosa ate dinner with Miguel, Carmen, and Johnny. She asked if he does one-on-one sparring with Sam during karate, since they are back together. In the third episode, she and her friends are inside the apartment and witness Johnny and Carmen together. During the prom pictures in the eighth episode, she tells Miguel that he looks more and more like his father, to which Carmen was not amused by. In the ninth and tenth episode, Rosa and Carmen watch Miguel compete in the 2019 All Valley Tournament. She sees Miguel pulling a muscle in his back, and later congratulates him for his fighting. Although Miguel decided to not return, they still watch the All Valley finals. After the tournament, she handed Johnny the note when Miguel left to Mexico.
Rosa is an extremely honest and straightforward person who tends to say exactly what is on her mind. Her frankness often embarrasses her daughter and grandson. She is very wise and perceptive, quickly assessing people and situations. She also appears to be a solid judge of character.
- Rosa has a very perverted and crude sense of humor, a stark contrast to her daughter, Carmen.
- Rosa appears to very little English or none at all, but can fluently understand the language.
- It is revealed that Rosa smokes joint in episode Mercy.