As the general manager of Shie Hassaikai, Joi is responsible for controlling and administering the business activities of his organization. He is often seen counting stacks of money bills, implying that he also plays the role of the organization's treasurer.

Joi, like all members of the Precepts, is ultimately loyal to Overhaul, and can become enraged if people show disrespectful or threatening behavior towards his boss. Joi is hot-tempered and easily lets his emotions run wild, even if it costs him his stealth advantage.