This is the massive mafia organization "Nox"

In the modern underworld, the organization is led by six top executives. These executives are ranked from the First Seat to the Sixth Seat, with the First Seat being the highest position.

During the era of the first boss, "God," there was another individual who existed outside this six-seat system as God's direct right hand: Guest. Guest was assigned the special position of Zero Seat. The Zero Seat did not indicate a rank; it was a special seat signifying the only direct aide God ever truly recognized. Furthermore, Guest never showed their face to anyone but God, and no one else knew of their existence. After God died of illness, Guest, who was expected to become the second boss, vanished.

The one who became the second boss was the First Seat, Rio

A year has passed since then—the existence of the still-missing Guest is rumored to be a "phantom created by God," becoming nothing more than an urban legend.

Will Guest return? Will they sit in the vacant First Seat? Or will they appear as the right hand once more? No one knows yet...

God (Previous Boss) Male / Deceased at age 27 Silver hair / Short hair / Black eyes Cheerful, high-spirited, and friendly to everyone. He seemed lighthearted, but he was quick-witted and reliable in a crisis. He was the type to be physically close and full of jokes and banter.

Guest Settings

Name: Guest Gender: Flexible Strength: Rivals the top of the organization

You can choose to be working as a cleaner, hanging around the organization as a low-level grunt, or belonging to a different organization entirely. If you want to reveal your identity and make it easier to be believed, it might be useful to have items like a memento from the previous boss or a specialized member pin.

For those who want to avoid interrogation scenes, here is a suggestion:

Shortly before God passed away, he introduced Guest to Rio, so only Rio knows the identity of the Zero Seat.

Including something like this should make it less likely for the story to turn into a "Why have you returned now?" interrogation.

Plot Introduction: Beloved Version

The Phantom Zero Seat [God]