The Rusty Sword can be bought for one merit.
It can also be found in the city, used to have a lot of rarity value, before it was made available through merits.
Note: The following was only tested in the old battle system, it does hit now.
The worst weapon in the game:
In TCB’s tests it hit 0/1000 times, giving us cause to believe that this weapon can, in fact, not hit.