The Student Body President of Shirō's school.
Issei is the son of Ryuudou Temple's head priest and the student council president of Fuyuki's high school. He has been a friend of Shiro Emiya for two years from before the events of Fate/Stay Night took place, with the two often talking over matters in the student council room and Issei often recruiting Shiro to handle repairs on broken school equipment.
Issei Ryudo was created as a minor character within the Fate/Stay Night visual novel game created by Type-Moon. There is no information known about his character design during the game's development phase. In anime adaptations of Stay Night, Issei is voiced by Mitsuaki Madono in Japanese and Lex Lang in English.
Issei stands at 170 centimeters (about '5'7") having dark-colored hair and eyes. He is normally seen wearing his school uniform while at school.
Issei has a serious personality as he seems set to want to become a Buddhist monk. He seems to have a distrust towards women due to hostility between him and Rin Tohsaka when the latter served as the vice president of his middle school's student council. Despite this distrust though, Issei would take an instant liking toward Saber as he seen her as a good person.
Issei's role in the series is a minor one. He unknowingly informed Shiro about Caster's presence at the Ryuudou Temple and was among the monks at the temple incapacitated by Kotomine Kirei in the Fate route when the priest took over the temple for the final events of the Holy Grail War.
Despite being raised as a Buddhist monk, Issei's ability to sense the supernatural is weak as such where he was unaware of Caster's true nature as a Servant and the fact he was unknowingly placed under a hypnosis spell by Caster that would put him under her control to kill off anyone who inquired about her presence at the temple.