A Factor of JUDA's Special Task Force, Satoru made his way into the organization due to his body being extremely weak since birth, thus dooming him to an early death if not for his link to her Machina, Hind-Kind. Serious and energetic, with occasional bursts of cheerfulness, Satoru acts as a subordinate and an admirer for Reiji Moritsugu, whom he considers the one who introduced him to future role as a Factor. Nevertheless, his fixation with Moritsugu borderlines romantic obsession, which occasionally costs him his focus and efficiency in battle. Satoru's androgynous appearance and stature have often had him mistaken for a girl, the subject of which gender is correct having become a running gag within the manga/anime series.

Yamashita's manga incarnation is more grim and somehow arrogant, convinced that all Factors are indeed murderers, though he strongly refuses the idea of being a killer himself, though this is not adapted into the series anime.

Yamashita's Machina is the heavy assault platform Hind-Kind. Bright yellow and very bulky, its primary weapon are its huge fists, which can be ejected at high speed and distance thanks to ramjets mounted on the wrists and long, flexible tendrils made of the Machina's artificial muscles. On its hands there are independent, detachable probes usable for reconnaissance, and on its shoulders are mounted two massive artillery cannons with extremely long range and destructive power, making Hind-Kind pretty similar to a movable gun battery. However, being highly specialized in long to ultra-long range support, this Machina is easily outmatched in close combat.