Wildcard coccus (ワイルドカード球菌 Wairudokādo Kyūkin?) is a highly virulent killer bacterium introduced in Shinyaku Toaru Majutsu no Index. It is a coccus-type bacterium as its name indicates, as such it is of spherical shape when it viewed under the microscope. There is no mention on what would happen if W. coccus infected a person, other than they would undoubtedly be killed.