To see the Secret Ending, follow these steps:
Only available once the True Ending has been seen.
During the second investigation, go to Tatsu Park, go north and open the hatch. The bloody bandage will be replaced with a mysterious orb. Touching the orb restarts the game from the very beginning right after being teleported for the first time. If you have unlocked at least 60 achievements, you gain access to Izumi's computer. Select Tennis and beat the computer at it. Then select Af %%2035sc @ctions and select Af $$2035sc @ctions 13. Afterward, select Developer Tools and type in the password: cHeWiNg gUm. Go back to Af$$2035sc @ctions and select Af$$2035sc @ctions 2.
Finally, select Database, search for Marcus in the database, and put in the password: end times. Now complete the game again with the true ending.
This unlocks the necklace on the main menu.