On the following page of our Devil May Cry 5 Guide, you will find a description of the fourth secret mission in the game.
Secret mission 04
Where to find it: Mission 05 - The Devil Sword Sparda
When you reach the warehouse, you will come across a scaffolding after some time, which clearly blocks the passage. You then have to summon the Nightmare so that it can, as in the previous mission, unveil the secret passage. You will then have to face a group of enemies. After the fight, climb the stairs to the top and launch the secret mission 04.
In this secret mission, you must defeat your enemies, not letting yourself be hit once. Luckily, V is a character who can stay away from enemies and summon allies to do the fighting for her. The key to success is, among others, the Nightmare, who will quickly deal with most enemies. But be careful, however, not to teleport too quickly to enemies and eliminate them, as you may be hit during the killing process. The prize is a fragment of the blue sphere.