Tadayasu Souemon Sawaki is the main protagonist of Moyashimon and attends an agricultural university in Tokyo as a freshman. His middle name is the yagō of his family home; it is usually omitted, and he is called "Tadayasu Sawaki". He is a childhood friend of Kei Yūki and his parents run a mold starter producer. He is able to see and communicate with bacteria and other microorganisms.