Excurse of the Golden Witch

In October of 1987, a 28-year old stateroom steward calling herself Lunon returns to southern Japan for a reunion with her three younger "sisters" after more than a year abroad. In the wake of an impossible occult library and mysterious, seaborne message finding their way into the public eye, a bygone piece of the sisters' history arises to the fore... and Lunon faces off with a unique challenge from the Golden Witch addressed directly to her.

[From Itch.io]