Note: This game is also titled Forbidden Siren.
Time attack mode:
Successfully complete the first two objectives on all levels in every scenario (78 blocks filled on link navigator) to unlock the first ending sequence. Then, press Square at the scenario selection screen.
Brain Cell Revival (Zuno) puzzle mini-game:
During Tamon Takeuchi's Day 3 03:00 level, a Brain Cell 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 appear at the main menu.
Hidden FMV sequence:
Successfully complete the game after finding all 100 Archives. A bonus FMV sequence will be unlocked at the top right corner of the scenario selection screen.
Mission Objectives 2:
To unlock Mission Objectives 2 for every character and/or scenario, complete 19 stages in any order. Then, press L1 + R1 while the stage is highlighted at the scenario selection screen. Note: You will automatically obtain it after completing the random 19 stages.
Hint: Break strangleholds:
If you get too close to a regular Shibito, it will sometimes prefer to grab you by the neck and choke you to death instead of doing a regular attack. When one takes you into a stranglehold, rapidly move the Left Analog-stick Up and Down. This will break the hold, and prevent you from dying.