Yoko Ritona, known to her friends as simply Yoko, was an extremely skilled soldier and sniper, and a long-time member of Blue Team. She was one of the most popular members of Blue Team, having joined them during the Mining Union War, and remaining on far beyond into the Rise of Chaos. Yoko was known as an exuberant, fearless young woman, famous for her positive attitude and her seemingly endless compassion for others.
Yoko was not only a hero of Earth with Blue Team, but she was also an excellent soldier and markswoman. Enlisting with the United Nations Space Command during the Mining Union War, she served in the Naval Marines as a Corporal, where she was ranked as the First Rated Sniper in the Galaxy, with numerous kills to her name and no missed shots. She continued her service to the UNSC up until the War of Pawns, where she joined up with Blue Team, and through her brave actions became known as a hero of Earth.
During her time with Blue Team, David "Solid Snake" Thatcher developed a strong infatuation for Yoko that eventually became affection and endearment. Despite their age difference, Yoko and David did engage in a relationship. Despite this, Yoko did not truly love Snake, instead she was deeply in love with her commanding officer in the UNSC, Major Jackson Briggs. Regardless, when the time came for the members of Blue Team to depart the world following the defeat of Chaos, Yoko agreed to bear two children with Snake; Ryuko and Zeroku.