All of our Blades to date are made from High Carbon steel and therefor are vulnerable to rust if not properly cared for. Multi-purpose oil such as 3-in-1 oil is what your berserk blade ships with. But gun oils, non-detergent motor oils, vegetable oil or even Mink oil will do the trick.
When not in use -, Re-oil the blade at least bi-annually if not quarterly to ensure corrosion isn't occurring. Storing the blade in a climate controlled part of the house or at least out of the basement will do wonders to preservation even without oil. If it does start to rust, let it patina and just use it or a brass bristle brush will do wonders too clean it up.
Cleaning - Clean the blade after each use, regardless of what you used it for. Wipe it dry and re-oil it when your done. Soap and water is suitable, if its just too grimy, but don't forget to wipe dry and re-oil.
Our Leather sheaths are usually stained to color and then always Mink oiled. We use a Mink oil that has a the color red and a Moose on the label; truly good stuff. We do recommend that you re-oil the leather annually to keep it alive. Remember, the blade and its sheath could be passed down through generations, if properly cared for, down to the next run of little Vikings.