Secret Missions are hidden missions during the regular missions that you need to find, that have a specific objective you need to achieve. In order to access them, you will need to locate some markings that form a circle on a wall, ceiling or floor. Once you have, you then need to stand in a specific spot that will help complete that circle, which is usually denoted as something red. When you’ve found it, look at the circle until you get the button prompt to begin the Secret Mission. Your reward for completing a Secret Mission will be a Blue Orb Fragment.
The first Secret Mission can be found during Main Mission 02 and it’s pretty hard to miss, as it’s right on the main path and even give you a tutorial about it. If you need some directions, it will be found in the hotel, in the room that is busted open after some Qliphoth roots break through the wall. The spot you need to stand on is behind the bed, letting you start the Secret Mission.
Your goal for this Secret Mission is to simply defeat all of the enemies. This is probably the easiest of the Secret Missions, since there is no strict rule imposed on you. You will fight three waves of enemies, starting with some Empusas. The second wave will consist of a Green Empusa and some Hell Caina, then the third wave will simply be a few more Hell Caina. Don’t worry about your Stylish Rank during this, as you should simply concentrate on finishing the Secret Mission.