In the world of VA-11 HALL-A, Cat Boomers are people who have gone through a certain process to prevent Nanomachine Rejection (a condition where the body violently reacts to the nanomachines within) in at-risk fetuses. As a side-effect of this process, subjects develop a pair of cat-like "ears" atop their head.

Initially, the term was used to refer to parents who had their children undergo the procedure just for the vanity and look the "ears" had. But eventually, use of the term shifted instead to refer to those themselves who had been subject to the process, rather than their parents.

The "ears" in question aren't even functioning ears, but are rather just lumps of cartilage, muscle, and skin, being the result of a mutation the procedure produces.

Known Cat Boomers:

• stella hoshii