The name of this game's hero is Ryuusuke; he has a fascination for ancient civilizations and archeology, researching them thoroughly in hope of finding legendary treasure. One day he has a strange dream after having dozed off in his office: he has found an enormous mythical treasure, which is guarded by a terrifying monster... when he wakes up, strange things begin to happen one after the other. Ryuusuke finds a mysterious ancient staff and decides to investigate its secret; beautiful golden-haired girl tells him he is on a a grand mission... Which is dream and which is reality? That is what the hero will have to find out...

DE・JA is a Japanese-style adventure. At every screen, a menu with verb commands appears at the bottom. The commands include Examine, Talk, Ask, Take, Use (an inventory item), Move, as well as other context-specific commands that appear on some screens. Choosing a verb usually leads to an object sub-menu. Typically, the game's story advances once the player has gone through most of the commands and acquired the needed information.

The game has some scenes with nudity and mildly depicted sexual situations.

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