The Carian Retaliation sorcery (not to be confused with the Ashe of War of the same name) can be purchased from Preceptor Selvius for 9,000 Runes. Preceptor Selvious can be found at Selvius’s Rise, in the Three Sisters region of Liurnia, past Caria Manor. Reaching him is hassle enough, as you must venture through Caria Manor, defeat the Royal Knight Loretta boss, then head to Ranni’s Rise and start her questline. If that’s not enough, you must also complete Selvius’s questline to get him to sell you his wares.
How to Get Through Caria Manor
From the Main Caria Manor Gate Site of Grace, enter the manor and immediately turn left; follow the wall here northwest and either avoid or defeat the Spider Hands that emerge from the ground to distract you. The Lesser Spider Hands aren’t strong foes, but they can be nuisances in numbers. You also need to be wary of the buried Spider Hands (their fingers stick out of the ground, making them fairly easy to spot), as if you get too close they’ll ambush you.
Go under an arch to the northeast and continue hugging the wall to the left, ultimately making your way northwest into a building guarded by Spider Hands, both large and small. Once inside you’re relatively safe for the moment, just head upstairs and you’ll find the Manor Lower Level Site of Grace.
Rest up and when you’re ready for the next phase go through the doorway to the southeast to reach some elevated walkways. While the walkways look clear now, as you traverse them some Phantom Raya Lucaria Soldiers will spawn, who fight very similarly to their corporeal counterparts. There are also invisible magical traps scattered about, but their activation delay means simply walking over them will allow you to avoid them.
Fight or run across the walkway to the southeast and when you reach a fork at a tower, continue southeast. When you reach a second tower, turn left (northeast) and head upstairs to find another tower, inside of which is a lift which will take you up to the Manor Upper Level Site of Grace.
Exit through a doorway to the northwest and be wary of some Direwolves. They may look like normal Wolves, but these specimens are much hardier. Fortunately you can just run past them; head northeast down some stairs and continue northeast until you spot some stairs leading up to a doorway to the northwest.
Things get rough through this doorway, as you’ll need to ascend some stairs guarded by Page enemies, along with a Troll Knight, who is a much, much more dangerous version of the Trolls you may have encountered elsewhere. Fighting them is dangerous, but you can, with some nerve, run past them and through a gate atop the stairs.
Make it past and you’ll find yourself in a large courtyard dominated by a shallow pool surrounded by chairs. Approach the pool and Royal Knight Loretta will appear. You’ll have to defeat this boss to continue, but fortunately there’s a Stake of Marika just outside the gate leading to the courtyard.
How to Start Ranni’s Quest
Once you’re trudged through the Caria Manor, exit via a gate to the northwest and look southwest - you should spot some towers in the distance: one to the west, northwest, one to the south, southwest and one to the southwest (possibly obscured by a tree). Your goal is this middle tower - the other two are sealed. Avoid Glintstone Dragon Adula roaming about and you’ll find Ranni’s Tower beyond the dragon, guarded by some lowly Wolves.
Enter the tower and work your way up to the top and talk to Ranni, accepting her offer to enter into her service. Next you’ll need to talk to her three servants, War Counselor Iji, Blaidd the Half-Wolf and Preceptor Selvius, then return to Ranni and talk to her again to lower a barrier surrounding Ranni’s Rise.
How to Get the Carian Retaliation Sorcery
Now that you’ve started Ranni’s questline, you can visit Selvius’s Rise, a tower to the southeast of Ranni’s Rise. Talk to Selvius to start his quest, which tasks you with giving a potion to Nepheli Loux, whom you’ll find back at the Roundtable Hold should you already progressed through Raya Lucaria Academy, sitting down the stairs from Smithing Master Hewg. You have an important decision to make here, if you decide to go along with Seluvis’s scheme and hand the potion to Nepheli, you’ll end her Questline, but in the process, gain a unique Spirit Ash from Seluvis in the process.
Your second option here is to wait until you’re beyond Altus Plateau and have the Dung Eater in the Roundtable Hold. Advancing his Quest far enough will allow you to feed him and should you feed him the potion, you’ll end his Questline, but get another unique Spirit Ash.
If you wish to continue Seluvis’s Quest and not void the other two, there is a third choice available to you: talk to Gideon Ofnir at the Roundtable Hold and mention Selvius’s potion, after which you’ll be able to hand it over to him to dispose of, tricking Seluvis into thinking you gave it to Nepheli, but it didn’t work. You won’t gain either of the two unique Spirit Ashes, but you will be able to continue all three Questlines.
Regardless of your choice, return to Seluvis and deliver the news, he’ll thank you and, in return, agree to sell you some Sorceries.