Jophiel's archangel blade or Ledan's archangel blade is one of the 7 archangel blades given to each archangel, specifically the one which belonged to Jophiel. Whilst the whereabouts of most are unknown, Jophiel's is in his son Ledan's possession. Each blade wields a great deal of power; similarly to the colt, angel blades or Ruby's knife, archangel blades can kill a lot of things normal blades, or even the above can.
It's essentially a more powerful form of the aformentined angel blade; as it, unlike the angel blade, is capable of killing an archangel or "archnephilim". It's because of this Ledan keeps it under lock and key, since it's the only weapon that can kill him.