Hollow Zero, also known as "Limbo," is a colossal Hollow that consumed the old Eridu, resulting in its destruction, and serves as the source of several massive Hollows in and around New Eridu.
The investigation and neutralization of Hollow Zero pose a long-term challenge for the authorities of New Eridu, both presently and in the future.

The Hollow Investigative Association will regularly issue commissions to investigate Hollow Zero and give rewards to those who complete the commissions.

Once you've explored the Core area, you can choose to continue your exploration into Withering Garden and challenge more powerful enemies for more lucrative rewards.