Wataru is a first-year university student taking up literature. He is the bassist and lyricist for the band Argonavis, and is the younger brother of Kenta Satozuka.

In stark contrast to the hot-blooded, idealistic, and optimistic Yuto, he is more cautious, realistic and pessimistic, often finding the negatives to Yuto's attempts to be positive. And yet, it's because he wants the band to be a success. He has an inferiority complex toward his older brother Kenta and wants to surpass him.