O-Jirō is a ghost (obake) and the youngest sibling in his supernatural family. His older brother is Q-Taro, his younger sister is P-ko, and his parents are X-zō (father) and O-zetto (mother). Physically small, he has a round, yellow body, black eyes, and a single prominent hair atop his head.

He communicates almost exclusively through variations of the phrase "Bakeratta," including "Naniratta?", "Baccaratta!", "Dummelerta," and "Aholachta." Only Q-Taro fully understands these utterances, leading to episodes where Q-Taro interprets O-Jirō's speech for human characters. Despite his limited verbal expression, O-Jirō comprehends human language.

As an obake, O-Jirō can trigger explosions by shouting "Bom!" or "Pa!", detonating objects or people directly in front of him. He displays notable dexterity and craftiness, excelling at repairing items, creating toys, and fashioning functional socks from materials like newspaper. His behavior often reflects that of a kindergarten-aged child, involving playful mischief.

O-Jirō shares a close emotional bond with Q-Taro. When their parents planned to take Q-Taro permanently to the obake world, both brothers reacted with visible distress and hid together. Witnessing their unhappiness, the parents reconsidered their decision, allowing Q-Taro to stay with the human family and O-Jirō. His design was featured in educational content, such as an outro sequence teaching viewers how to draw him.