Rosemary (usually referred to as Rose) is a supporting character in the video games Metal Gear Solid 2: Sons of Liberty (2001) and Metal Gear Solid 4: Guns of The Patriots (2008), she is also mentioned several times in Metal Gear Rising: Revengeance (2013). Her first appearance, in the Plant episode of Metal Gear Solid 2, was November 13th 2001. Her main role in both games is to provide support + insight via codec: in MGS2 she is a data analyst who handles saving the game and offers her input on the mission or on her personal affairs with the protagonist of the game. In MGS4 she takes the role of a psychological counselor and offers advice on how to manage the psyche gauge. In the PAL and Japanese releases of MGS2, if you select '1st Time' when starting a new game, a voiceover of Rose will walk you through the options and introduce the game before it begins. She is the girlfriend, and later wife, of Raiden, who is the father of her son, John.
In terms of the story, Rose was born sometime in the early-to-mid 1980s, I personally put it at 1985. She worked at the Pentagon as a data analyst before being recruited by The Patriots (a secret organisation controlling the United States) as a spy. During her time undercover she worked as an analyst for the U.S. Army and was stationed in New York. She was tasked with aligning herself with the tastes of a U.S. soldier named Jack (later known as Raiden); to get into a romantic relationship with him and find out information about his past - a past which was kept classified and off-record and was never divulged to others by him. She met Jack on the 30th of April 2007 in front of Federal Hall. Jack had interrupted her while she was giving out incorrect film trivia (whether King Kong climbed the Chrysler Building or Empire State Building) to a group of tourists, causing the two to argue over who had the accurate recall. A week later, they met by surprise on the military base they both worked on, and that night went on their first date to the top of the Empire State Building.
Over the course of the relationship, she began to develop genuine feelings for Jack and felt remorse over the circumstances controlling their relationship. She chose not to disclose certain things she learned about Jack to her employers and later confessed to being a spy on the two-year anniversary of their meeting after she finally learned of the truth about Raiden's childhood as a child soldier in the First Liberian Civil War. She also revealed that she was pregnant with his child. Due to the unplanned confession, she is suddenly taken off air and replaced with an AI that replicates her voice and appearance in order to insult and dissuade Raiden. It's revealed that her nanomachines are linked to Jack's: if he fails his mission and dies, so does she. During the finale of the game, the two reunite in the streets of New York City and decide to continue their relationship, this time seeing each other for who they are instead of playing false characters.
As memories of his past and the Big Shell mission weigh on him, Raiden becomes more withdrawn and unstable, drinking heavily and eventually leaving home for good; abandoning his duties, Rose, and his unborn son to wander the earth alone. In order to ensure the safety of their son without Raiden's protection, Rose conspires with Raiden's commanding officer. They stage a false marriage and pretend that Rose had miscarried Raiden's child so they were no longer viable leverage against him. There's a vagueness in how this played out: in some translations it's implied she lied directly to Raiden; in the original it can be taken that Raiden heard it from an outside source. Without getting too into it, I find the version where he found out from somebody else after he left to be more accurate. Sometime during this period, Rose returns to school to study psychology and becomes qualified as a counsellor. She begins working to provide psychological support and stress-management techniques to combatants on the battlefield.
At the end of the fourth game, she visits Raiden in the hospital and introduces him to his son, assuring him that what he heard about the miscarriage was a lie. There, they reconcile and decide to try again as a family. Raiden promises he will never leave her alone again.
Things after this are unclear as Metal Gear Rising: Revengeance is somewhat debatably canon. However, it's suggested that she supported her family with her work as a psychologist during the recession where Raiden struggled to find employment as a cyborg. He later gets a contract with a private military company to send money back to his family. This money meant that Rose and John could move out of the country to live in safety in New Zealand. In the game's codec calls, Raiden speaks of Rose and his son entirely positively, as well as preaching the happiness marriage and family has given him to his codec team, implying they've worked things out between them.
Unfortunately most of her canon character arc is centred around Raiden, and very little is known about her backstory or her as a person. In a way, this fits the theme of her shunning her own self in order to carry out her assignment playing a character Raiden was most likely to fall for, and perhaps there's a deeper meaning behind that (but I would put money on women just being written Like this throughout the series...), but it's still disappointing that there's so little given.