This is the one of the easter egg in the game that could get an achievement, might contain spoilers? View it on your own risk!
The first step obtaining the key!
You need to parkour to the top for a chest that gives a studio key and you might need a lot of attempts and careful while you come back down cuz of fall damage. Falling off would only deal damage on normal mode tho, I don't know on hard.
Second step. Defeat the boss that look like a demon or bull, try not to die, below one is the studio room just go there before going up and pass the level, make sure to check properly cuz there are obstacles you need to destroy before you go in the studio.
There is a locked door on the right, use the key you tried so hard to parkour to open it, talk to the ceo or director and check the garbage can and the side of the wall, you would see the sword I have and the cat suit I am wearing, also speak to everyone in the studio to gain some blood essences and there might be loot laying around the studio. You would unlock the easter egg achievement only if you unlock the door on the right.