Poison Master Hikaru Gero is about to take on his most challenging assignment yet -- getting married! But after training his entire life to become one of the world's deadliest assassins, Gero couldn't be more clueless when it comes to the art of dating. Thankfully, marriage swindler Mei Kinosaki knows everything there is to know about love, and together, this unlikely pair is going to do whatever it takes to get Gero hitched -- even if they have to take on the entire criminal underworld in the process! After assessing Gero's romantic qualities (or lack thereof), Kinosaki decides the best strategy to find Gero a wife is to use his impressive talents as an assassin instead! Together they respond to a job listing to rescue Himekawa, an art thief who's been taken hostage -- but with a water master now standing in their way, their plan takes a turn for the worse! Can Gero win this fierce battle of poison versus water and take his first step toward marital bliss?