The Blade of the East has an effect of -2 hp for 10 seconds. It appears that the only cosmetic difference between The Blade of the East and a bumper sword is that it does not have a license plate on the underside of the sword. Legate Lanius can be seen hitting NCR (non-veteran) rangers with it, dismembering and getting one-hit kills. The weapon can also cause your enemies to fly backwards and be knocked out.
Can be looted from Legate Lanius in the final battle if siding with the NCR, Yes Man, or House. Note that you will only have a limited time to use this, as the game ends soon after the fight. Assuming you fight for independence, it can be used to great effect against Oliver and his Rangers.
The Legate has a different version of this weapon (confirmed by the GECK) that is not meant for the player to have, as when the player attempts to take the weapon from the Legate's corpse, a "Blade of the East" is instead added to the player's inventory.
Lanius' unique version of this weapon has a base damage of 65, a critical damage of 30, and a damage per second of 102. Lanius himself often inflicts more than 100 points of damage per hit with his sword.
Unless siding with the Legion and pickpocketing (high Sneak skill required) from Lanius, you only have a limited amount of time to use it due to the story ending immediately after.