Marriage Toxin, Vol. 3 (manga)

Gero pushes his assassin skills to the limit when Kinosaki signs him up for the job of bodyguarding Shiori Ureshino, the daughter of a high-profile CEO. He’ll need to go toe to toe with Sound Master Naruko, a rival assassin, in order to protect Ureshino and prevent Naruko from turning her university camping trip into an all-out horror show!