There's a wonderful tradition of secret endings in games. There's the Far Cry 4 ending where you just do as you're told and avoid hours of hardship, there are others of note too. Far Cry 5 kept up the tradition and you can now add Devil May Cry 5 to the list.
During the course of the story you come up against Urizen multiple times. He is the embodiment of demonic power and is only supposed to be beaten once you reach the correct point in the story. For the most part, you aren't meant to win. These are fights designed to show you the difference in your power—to demonstrate how far from being a threat you are. The first of these happens in the prologue when you're playing as Nero.
At this stage in the story, Nero doesn’t even have his Devil Breaker arm let alone his Devil Trigger. However, if you come back after you have finished the story (or if you are preternaturally gifted) you can actually take down this big bad the first time you meet him, making this game around three minutes long—not including cutscenes.
The easiest way to do this is to take down the shield protecting him without using any of your Devil Trigger. Once you have done this, devil suit up, get in close, and just hammer away at him as quickly as possible. We found the best way to do this was to just stay near his head and hammer away at X and Y, or Square and Triangle. You can then finish him off just before your Devil Trigger runs out by letting go of the lock-on and hitting right trigger or R2. That should make demonic mincemeat of him and put him back into the pages of William Blake where he belongs.
If you manage this, you're treated to a little bit of text about how everything worked out fine, there is a new legend in town, and you get an achievement too. It's one of those little bonuses you'd only figure out if you were a glutton for punishment—or if you happen to read our guides.