A teenage girl named Monica has been training all her life to carry on her family's deadly assassin heritage. Her first assignment is to go after the Dirty Pair. Kei and Yuri go to a vacation resort to relax but soon find themselves on the guard as bombs, traps, and deadly attacks appear wherever they go.

A felon sprung out of prison transport makes a deal with a crime boss to command and pilot an advanced assault mech, but first he wants to borrow the mech to go after Chief Poporo of the 3WA. Soon afterwards, bombs start going off all over the city and the Chief's life is in danger as the mech raids 3WA Headquarters. Kei and Yuri try to protect him, but what complicates things even more is that the Chief's daughter is at the office for a visit.