Yoshimitsu is a character from Namco's Tekken game series, but also starring in Soul Calibur for Dreamcast. He usually wears an armor resembling a samurai uniform and a mask of Rannya, a japanese demon with a diabolical smile.
In Tekken, he is a space ninja with a lightning katana and his outfit may change from classic to insect (something like Kamen Rider) or he may use a skull shaped mask. But in Soul Calibur he is the chief of a thieves' guild and he uses an ordinary katana and a turban.
When he wins a fight, he says things like Shiki Zoku Zeku and other old proverbs full of kanji, hence difficult to translate. I remember this particular one was translated to "Your life is in vain" in the US.
His special opponent is Kunimitsu, a woman ninja with a lightning dagger and a Hello Kitty mask.