The legendary Mantis Blades are some of the most powerful weapons available in Cyberpunk 2077.
There are two locations in Night City that harbor chests containing Legendary Mantis Blades. One is in Corpo Plaza where the gig "Cyberpsycho Sighting: Phantom of Night City" takes place. The other can be found in Heywood during an "Assault In Progress" on the rooftop of a building.
Cyberpunk 2077 Legendary Mantis Blades: How to Get
The simplest way to obtain a pair of Legendary Mantis Blades in Cyberpunk 2077 is to travel to Corpo Plaza and go down the alley where V encounters Norio Akuhara in "Cyberpsycho Sighting: Phantom of Night City." There is no need to fight Norio or any other enemies to obtain the blades. Simply walk toward the chest that sits to the right of the alley near a garage door. The blades will not always appear in the chest but will be inside the vast majority of the time. Because of this, make sure to save the game before heading down the alley in case they do not appear. These Legendary Mantis Blades can be obtained early in the game and at any character level, but Norio poses a serious threat, so be cautious when engaging him.
A more difficult way of finding Legendary Mantis Blades in Cyberpunk 2077 is to travel to an "Assault In Progress" marker near Megabuilding H2 in Heywood. After climbing onto the rooftops, V will come across a situation where an EMP has brought down a Trauma Team ship. Amongst the wreckage, there is a chest containing a pair of Legendary Mantis Blades. The enemies in this area are high-level, so proceed with caution when seeking out the chest.
Once you have obtained the Legendary Mantis Blades, V must visit a Ripperdoc to have them installed before they can use them.