Wataru Matoba is the bassist and primary lyricist for Argonavis, shaping their musical identity. His childhood featured parental absence; his mariner father and nurse mother were often away, leading to heavy reliance on his older brother, Kenta Satozuka. This dependence fostered a deep inferiority complex after Kenta's musical involvement inspired Wataru to play bass. Resentment grew, fueling his drive to surpass his brother.

Personality-wise, Wataru exhibits a cautious, realistic, and often pessimistic outlook, contrasting bandmate Yuto Goryo's optimism. This tendency stems from a strong desire for the band's success, not mere opposition. Academically, he studies literature at university, sharing this faculty with bandmates and acquaintances, aligning with his love for reading and lyrical craftsmanship. He named the band "Argonavis," inspired by the defunct constellation Argo Navis, and crafts their original lyrics.

His character arc focuses on reconciling personal insecurities with collective ambitions. During Argonavis's relocation to Tokyo for the LIVE ROYAL FESTIVAL, he expressed uncertainty about their aspirations to reach "the world," reflecting his habitual wariness. His relationship with Kenta remains strained despite occasional band-related interactions, marked by emotional distance and unresolved tensions.

Physically, Wataru stands 175 cm tall, weighs 64 kg, has auburn hair and grey eyes, and was born on April 22. His development portrays an ongoing effort to channel insecurities and critical perspective into constructive band support, using music toward self-acceptance and reconciliation with his past.