To fully upgrade the Blades of Chaos in God of War (2018), you need Chaos Flames and a Raging Inferno of Muspelheim. The maximum level for Blades of Chaos is level 5. It can be upgraded at every shop.
The blades start out at level 1. The Chaos Flames for Upgrade Levels 2-4 are automatic drops from story bosses. They cannot be missed, just beat the story. Even if you don’t pick them up from a dead boss, they will be placed in the “Lost Items” section at every shop.
The last upgrade makes an exception and wants you to trade in the Raging Inferno of Muspelheim at a shop to get the Chaos Flame material in exchange. You must have beaten the story to perform the final upgrade.
How to Get Raging Inferno of Muspelheim:
Short version: it’s dropped by the Valkyrie in the Realm of Muspelheim.
- Start by unlocking the Realm of Muspelheim. For this you must find 4 Muspelheim Language Ciphers in purple chests. You can find a video with the cipher locations below or refer to the text/screenshot version How to Unlock Muspelheim Realm.
- Once you reached Muspelheim, you must fight your way through 5 challenges to reach the top of the mountain. You must beat each trial twice – one time the normal version, one time the hard version. This unlocks a gate to let you advance further up the mountain. At the top of the mountain is the Valkyrie.
- Defeat the Valkyrie. She drops the “Raging Inferno of Muspelheim” resource item.
- Go to any shop > Buy > Resources > Chaos Flame. This exchanges the Raging Inferno for the item you need. Now in the shop go to Upgrade > Blades of Chaos (you must have beaten the story to exchange the item).
All done. After the story your Blades of Chaos can be fully upgraded to maximum level (level 5). This also unlocks the trophy “Why Fight It?”.