Marriage Toxin, Vol. 2 (manga)

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 vs. water and take his first step toward marital bliss?