The dark organization WSP threatens the world. In response, the International Defense Agency was formed by those aware of its existence, establishing branches across nations and dispatching investigators to eradicate WSP. In Japan, the system is fully operational, and investigator Mako continues her streak of defeating the serial killer machines created by Johnson, president of WSP's Japanese branch. However, investigators battling WSP worldwide suffer under its overwhelming power and are being eliminated one by one. Amid this crisis, Mako faces her greatest challenge yet. After defeating WSPJ003 and seizing the return circuit, Mako infiltrates President Johnson's hideout, only to come face to face with the ultimate killing machine: WSPJ004! Possessing speed and strength far beyond any previous enemy, WSPJ004 relentlessly overwhelms Mako. Can Mako defeat WSPJ004—the masterpiece created by President Johnson—and restore peace to the world?