EASTERN PROMISE Trophy in Not A Hero
FIND THE SECRET DOOR IN SUSHI CENTRAL
How to unlock EASTERN PROMISESushi Central is the third and last section of the game, where Days 15 to 21 take place.
The secret door is located in Day 16 "Ninjery Time". Just progress normally until you find the first door that you need to blow up with C4. Once done, move up one floor and you'll see a red barrel at the far left. Execute the guy next to it, position yourself on the left side of the barrel and shoot it. This will send you flying to the secret door, just go through it to unlock the trophy (you don't need to complete the bonus stage). If you prefer visual help, please see the video below.