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 Yuuki and his parents run a mold starter producer. He is able to see and communicate with bacteria and other microorganisms.