I'm in Love with the Villainess (Manga) Vol. 6 (manga)

Rae is delighted when Claire decides to spend summer vacation in Rae’s hometown of Euclid. She’s extra delighted when she gets to see Claire in a swimsuit! But their fun is cut short when a ghost ship drifts into the harbor crewed by the undead! The girls will need to use their magical abilities to protect the city, but they soon realize that there is a traitor close to them! Can Rae figure out who it is in time?!