After the events of ''Sukeban Deka III'', the 17 years-old Saki Asamiya III, Yui Kazama (Yui Asaka), works for the Juvenile Security Bureau, an expansion of the Sukeban Deka project. This organization is led by politician Kuraudo Sekin (Masaki Kyomoto), who fights Juvenile delinquency in drastic manners that include summary executions, exemplified by his student agents's triple-bladed yo-yo weapons. However, when Sekin's methods become too zealous, Yui quits the bureau and refuses to undertake undercover missions for them.