箱 - Japanese Spelling
Well, since it is a Hentai game, you must've already understood the goal of the game: get sexual with this girl. In different ways. For those who care about the size: the protagonist will be able to adjust his own size to the girl's if the player wishes so. Or, he can play a "Lonely and sick Gulliver has captured a female Lilliputian for his perverse pleasure". In any case, it's not as simple as it sounds. Even though the girl is tiny, the protagonist is a gentleman (to a degree) and wouldn't do anything unless the girl agrees to. Lift up her skirt too soon and you'll get slapped, forcing to start again. Various means are at the protagonist's disposal to try and capture the heart of his lovely prisoner. He can buy clothes for her, feed her, buy furniture and objects for her room, etc.
The gameplay inside the room (outside of it you can access the computer to go online shopping) is standard Illusion fare, known from Des Blood series and pretty much every their game since: moving the camera in full 3D environment, the player interacts with the girl by choosing commands (touching specific body parts etc.), and then performs the action in real time by moving the mouse. The intensity of the mouse movement determines the intensity of the action performed on screen.
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