Dai Daichi is the youngest and most hyperactive member of the Daichi family, an impulsive elementary school student who dives headfirst into actions without thinking. His reckless behavior frequently sparks trouble, cementing his role as a mischievous prankster who uses outrageous antics to find laughter within their dysfunctional home. He chafes against the family's strained dynamics, often clashing with his older sister Nozomi over her attitude, though flickers of underlying loyalty and care for her remain.

Assigned by the Galaxy Federation alongside his family to defend Earth, Dai eagerly joined the force, relishing the chance to battle extraterrestrial threats. He tackles missions with reckless, headstrong abandon, charging into fights without strategy. This impulsiveness spills into his school life, manifesting in attention-seeking stunts like skirt-pulling. His unusual alien pet, "Weird," underscores his connection to the bizarre.

During defense missions, Dai's actions inadvertently aid the family's slow reconciliation. Confronted by external dangers and shared responsibilities, his fierce protectiveness surfaces in crises – most significantly in the finale, where he races to retrieve a vital flower to cure Ellen Shiratori, their alien ally suffering a severe allergic reaction. This decisive act reveals a determined resolve beyond mere mischief. His journey traces a shift from chaotic individualism toward embracing his place within the family unit, while retaining his whirlwind energy.