The plot directly follows the events of Rance 4.1, where Rance and Athena 2.0 solved the case of monsters appearing underneath Happiness Pharmaceutical, the company responsible for producing the world-famous Seirogan healing drug. Partie Burr, captain of the Angel Army Rabbit Group, was captured in a failed assassination attempt against President Doharas Happiness; while Arnie Rolento, revealed as another captain, escaped. Partie threatens that Archibald and her comrades from the Angel Army would arrive to save her, and finish the job; worried about this, and prodded on, Doharas hired Rance's party to destroy the Angel Army for 200,000 gold. Genri the monk, still searching for his brother, decides to follow them; along with Kisara Copri, who wants to thank Rance for helping her repay her debt to Pluepet. After sexually torturing Partie for information, Rance's party discovers that the Angel Army's main base is hidden below the idyllic Romance Park. With some rough investigation, they unearth a hidden path through a sandbox. Unbeknownst to them, Arnie is observing the group's every move; and has not only prepared the Angel Army for battle, but hired the four warriors known as the Marishiten Assassination Brigade to kill them. Another group is out to kill the adventurers, who she'd rather keep hidden: the Rare Gal Monsters Sailor, Blazer, and Jumper, seeking revenge for their rape in Rance IV. Aside from them, the homeless dog master Gotou considers Romance Park his territory, and will not stand for intruders trying to conquer it. Aided by the mysterious Pink Mask, and with the restrained Partie still holding secrets, the team of four raid the base. They must discover the truth behind the Angel Army's attack on Happiness Pharmaceutical and the disappearance of the Holy Monster Gal Wenlina - all while Rance is set to deal revenge on Arnie for her treachery, get a moment alone with Kisara, and collect his much-needed reward money.