Based on the erotic game by Guilty.

A cruise with only guests invited by a famous company and staff allowed on. This cruise, the Northern Light, is celebrating it's 200th voyage, with Fujigasaki Miho's father as the captain.

Miho is invited by her best friend, Moribe Jun, to work there part time.

Otowa Saki, a student working at the cruise's restaurant, playing the violin. Kurusu Nonoka, an idol holding a handshake event on the main deck. Fujigasaki Miho and Moribe Jun, who are working at the casino as waiteresses. And Mizunashi Nadia, a dealer at the casino.

We'll have lots of fun, and it'll be a great memory of how we spent our summer vacation... That's what Miho thought, before she realized the nightmare that was waiting for them.

(Source: hanime.tv)