Getting access to the Double Jump ability in The Last Faith is important for end-game exploration. There are a few steps you need to do to get it, but here's an easy-to-follow guide for you to follow.
How to unlock Double Jump in The Last Faith
In order to unlock Double Jump, you first need to progress through the game enough to reach the Ordens Regnant Palace zone. This is a rather late-game area, so if you have not come across it yet, don't worry. You cannot miss it if you're looking to finish the game.
Reaching this area is a task in itself, but once you do, you'll need to defeat Manfredd the Accursed, located in the heart of it. Of course, it wouldn't be a Metroidvania game if you could just waltz into his lair. A large, gothic door blocks any unauthorized attempts to reach him, so first you'll need to open it (the hard way).
Notice in the above screenshot that there are four torches hanging from the door. All four of these torches need to be lit in order for it to open. To light them, you'll need to locate four braziers within Ordens Regnant Palace.
These braziers are an absolute pain to find as the palace is a winding maze of traps and enemies. Additionally, you'll need the Ordens Palace master key to reach all of them. Fortunately, I've created a quick visual map for you to follow that will lead you to the key, the door, and the four braziers.
Once you've obtained the key and lit all four braziers, head back to the door, which should now be open. Head inside, and prepared to face Lisa as a boss encounter. Lisa isn't very difficult, so you should be able to dispatch her fairly quickly. After doing so, continue onward where Manfredd the Accursed is waiting for you in his lair.
Killing Manfredd requires a fair bit of finesse, as his attacks are massive and deal constant Frostbite status damage to you. The fight is a patience game. Attack only after Manfredd has attacked recently. Being frozen is a death sentence in this fight, so aggression must be limited if you're looking to score a victory. It took me several tries to bring this beast down, but if I can do it, you can too. If you're struggling, it's likely because you haven't upgraded your character enough. Make sure to also have enough Healing Injections for several attempts at the fight.
Once Manfredd has met his end, venture further right into his lair where you will find an ornate chest. Open this chest to obtain the Celestial Larva, which is the item that allows you to perform the Double Jump at will. Like previous function upgrades, you do not need to equip this item to have access to its effect. Now you can go explore those seemingly out-of-reach areas you passed getting to this point.
For more quality guides and useful information on The Last Faith, check out How to upgrade weapons in The Last Faith right here on Pro Game Guides.