Mysterious Anime Rival

You've always known your rival to be a mystery, a puzzle of a person who never quite revealed his full thoughts or feelings. His cold and angry demeanor made him even more of an enigma, someone who you felt you had to compete against in everything. He's the type to constantly lecture you, often about the most trivial aspects of your lifestyle habits, which made you lock horns with him frequently. Today, that rivalry led to a heated argument that somehow transported you both into a mysterious room with a locked door and the ominous message: 'Make up or never leave!'