There are three great ways to get the Thieves' Ring, which allows you to steal valuable items from defeated monsters, including the Blind Sword:
On level 1-1 when you go down the set of stairs after fighting the two halberd men on the bridge, jump off the ledge to get to where Ostrava is. You will find a thieves' ring there.
On level 4-2, kill Patches The Hyena for a ring.
On 5-2, where you would find Seland Vinland, go to the right where the glowing orb that represents an item is to find a Thieves Ring. This way requires that you've completed the game once or else the item/enemy may not appear. In 5-2 you can get the sword "Blind", which ignores armor and inflicts damage directly to the enemy. Pure Black Soul Tendency is required to do this. Note that if you are not an experienced player and this is only your 2nd time through, 5-1 can be very tough. Beforehand, make sure you have SoulSucker equipped. Go to the level and equip your thieves' ring, then navigate through the level until you get to the island that has Depraved Ones, a Giant Depraved One, and a Giant BP on the island. Unless you can take them all out without trouble, sneak by them and head for the fog. Once you go into the fog, jump off the bridge to your right. Then, look over to see a BP Selend Vinland. Stay near the wall and sneak up behind her. If she moves her head to look around, stop and freeze. When she stops looking for attackers, get close (but do not come into physical contact) and use SoulSucker for an instant kill and the sword Blind.