The second rare blade is Poppibuster and it can be obtained via a quest, although it will only be accessible to players who have purchased the expansion pass.
T-elos Re is a rare blade reserved for players who have cleared the game.
You’ll also have lost countless hours of your life playing through the game, so that should also tip you off.
The blades will be coming to the game on April 27 in update 1.4.0.