During Tamon Takeuchi's Day 3 03:00 level, a BrainCell Revival mini-game can be found in a child's grave when you switch over to Kyoya Suda. Successfully complete the level then save the game. An option to play a new puzzle game will now appears at the main menu.
Complete the game w/ the 2nd ending & collect all 99 archive items to unlock the 100th item. Go to the Stage Select screen then move the cursor to the upper right corner, and start the movie.
You can lock the classroom, faculty, and library doors. All you have to do is after you go through a door, turn around and open the menu (triangle on default configuration) and hit lock door. Warning: A shibito may still open the door after it hits it 4-6 times, and if you have a shibito after you it may open the door while your locking it.
Acquire archive 087 on Kyoya Sudo's stage, Day 3, 03:00 to unlock the Puzzle Game.
Complete the first 19 missions in the game and this feature will activate.
Finish every scenario, and objectives one and two for all stages to unlock Time Attack Mode.