Used to refer to a work (often an animation, but can be otherwise) in which all the characters are fundamentally the same recycled design. Name refers to Japanese character designer Hisashi Hirai (Scryed, Gundam SEED) who has become notorious for designing entire casts using all of 3 different facial designs.
"What the Hell? I can't tell any of these people apart! This artist has a serious case of Hirai's Syndrome going."
by DrugLordKai January 10, 2005