Nejimaru is one of three robotic protagonists defending Earth against the invading Baddaru Corps—alternatively called Baddle or Bugroy in regional adaptations. This character operates within a trio alongside Sombrenosuke and Drum-Kan-Bē, all repurposed gardening robots now dedicated to planetary protection. Their core mission centers on shielding humanity from extraterrestrial threats emerging from outer space.

Nejimaru's design integrates stylized robotic components, notably a dot-matrix LCD screen that conveys emotional states. This display functions as the character's primary method of non-verbal communication and expression.