Theresia is a psychological horror visual novel adventure game from a first-person perspective, consisting of two stories, each sharing a common background: an unnamed country, presumably under strict martial law by the time the game takes place, is engaged in a fierce and bloody war with an unspecified opposing nation.
Throughout the course of the game, both characters have to explore their confinements, trying to escape and learn the details of their past, avoiding traps and coming face to face with personal demons and other psychological dilemmas along the way.