HBD

HBD (unknown acronym meaning) is a disease from the MegaMan Battle Network series. There are 2 known cases of it, Hub Hikari and Mamoru. The first case "died", and the latter survived thanks to advanced technology. Symptoms include severe chest pain, and being unable to breathe. It is so rare, the only place they could've tested Mamoru for HBD was at Seaside Hospital. There are no curing medications as a bacterium or virus could not have caused Mamoru or Hub Hikari to have such severe chest pain; it is likely a hereditary disease/disorder. The only treatment and possible cure is surgery, but the procedure name is never revealed.

Trivia
The meaning of "HBD" was never revealed, but there is a theory by fans that HBD means "Heart Bypass Disorder". HBD is called such because the symptoms are like a typical heart attack, but worse.