Ore wa Kanojo no Mendoumi ga Ii

Shiho, the main character's classmate, has been confined in a ruined building. It's only the main character who knows about this. He goes into the building to save her, but is actually full of evil ideas... He tells her to do erotic things to him, showing a bottle of water in his hand. Shiho really wants to drink water, so she reluctantly accepts it. Like this, his requests gradually get bolder...