Seiji Matsuyama (松山 せいじ, Matsuyama Seiji; born April 28, 1975) is a Japanese manga artist from Fukuoka Prefecture. He is known for drawing many works featuring women with extremely large breasts, and he himself refers to himself as a "boobie manga artist" in his doujinshi and other publications. He is married to fellow manga artist Sayu Matsuyama (松山 紗夕, Matsuyama Sayu).
Source: “Seiji Matsuyama”, English Wikipedia (CC BY-SA 4.0), excerpt