Another old yuri manga, from the 70s. The character designs are quite similar to those of Shiroi Heya no Futari.
It's a horror story, in which the main character and her family go to their summer house for vacation and people start dying one by one. The twist is that the main character, Reina, is falling in love with her mysterious neighbor, Maya. But who is Maya really, and how does she know so much about Reina's family?