Glass no Mori is a PS2 Otome Game published by D3 in their Simple Series (the full title is Simple 2000 Series Vol. 13 The Love Adventure For Girls -Garasu no Mori-) . The main character is making a last visit to her deceased grandfather's house, on the edge of a forest in the countryside. The forest is rumoured to be a 'kamikakushi' that steals away children, so none of the locals go near it. The main character used to go in it all the time, but was told by her grandfather to stay away.
When she returns in the game, she takes a walk in the forest and sees a mysterious young man. Later, she gets lost in the forest, and comes upon a small café. Inside she finds the same young man, as well as two others, and the owner. They welcome her, but seem to want her to leave quickly, and they make several obscure comments on being trapped in the forest.
The possible love interests can be separated into 'forest' characters and 'normal' characters. The 4 'forest characters are the 3 young men and the café owner. The 3 'normal' characters are a boy that the main character used to play with, his older brother, and his brother's friend. As the main character, you learn more about each character's story if you choose to spend time with them, and you eventually learn (if you pick one of the 'forest' characters) that they were stolen away by the forest, and can't leave it. They are being pulled to a door somewhere in the forest that leads to an unknown place that they simply call 'the other side', and your goal is to save your chosen character from going there.