The Aquamarine Dagger is a curious weapon to acquire in the Dreg Heap. It has been fitted with a crystal imbued with magic power, which it can unleash and then crystallize as a sort of blade extension from short sword to long sword. The dagger’s description also suggests that it was a parting gift since it is engraved with an idiom praying for safety. We can thereby conclude that it was created by a crystal sorcerer as a present for a close friend or relative that was preparing to depart for somewhere decently far away and potentially dangerous. It is found off the corpse of someone unfortunate enough to be crushed beneath a collapsing Lothric rampart, so the first candidates to come to mind are the Crystal Sages or their apprentice Kriemhilde, but this is incredibly unlikely. The only instances where any of the three potentially travel far is when the Crystal Sages first come to Lothric and when one of the twins leaves for Farron. If it is the latter, then the blade should have been with the sage in Farron. If it is the former, then why only the one blade when there are two of them? Even ignoring all that, the actual phrase engraved in the blade is written in an “old language”, meaning it well predates contemporary figures.
Dagger inlaid with an aquamarine crystal.
It was something given for setting off, right? An idiom that prays for safety is engraved in an old language.
Battle Art is “Crystal Blade”. Unleashes magic power shrouded in aquamarine and temporarily creates a blue blade of crystal. That blade is long and can be wielded like a straight sword.
With this added criteria of someone ancient in mind, the original owner of this blade was probably Seath, the founder of sorcery whom all crystal sorcerers ultimately derive their craft. That being the case, the most likely recipient of the white dragon’s gift is Shira. The daughter of the Duke was sent from their home in Anor Londo to the Ringed City to serve as Filianore’s attendant and bodyguard, placing her in the region where we acquire the aquamarine dagger. And the bival pearl shows that the paledrake had at least at one point shown some measure of affection for his child. Therefore, Seath had more than likely created the blade to express his hope that his daughter would be safe traveling to the end of the world during such a trying time. In that case, why is the blade presently found in Lothric ruins when Shira has been locked in a room with a mad king long before that?
It is feasible for the knight to have not kept the dagger on her person when she first skewered the king and secluded herself to a dark room. It was a loving gift, but Shira already had to a spear and a clear preference for miracles over sorcery. She simply has no incentive to carry another weapon on her after she has already arrived at her destination. And so, Shira would have probably left it in her personal quarters at the Ringed City, ripe for the taking. The corpse carrying the dagger lies behind one of the Harald Knights, and more can be found in various parts of the Dreg Heap outside of the Ringed City. If these knights managed to infiltrate the city and later escape to these ruins as the lands coalesced, then it is completely possible for a thief to do the same. This burglar stole Shira’s dagger while she was away and then fled, only to be killed by the crumbling environment. Such random circumstances likely weren’t the developers’ original intention, however.
Cut content confirms that Shira would have confronted us with another character named the “Lady Attendant’s Retainer”. (侍女のお付き) The knight is referred to as Filianore’s lady attendant, and otsuki similarly refers to an attendant of a high-ranking person — such as a Duke’s daughter. Evidently, Shira would have brought one of her own servants with her from Anor Londo. This companion dresses in old Oolacilian attire, matching the previous implications concerning the gods’ human servants in the original Dark Souls. And befitting a servant of Seath, the Oolacilian also casts crystal sorcery via Logan’s staff, though it is probably intended to just be a generic wooden staff of great power in this particular case. Regardless, the attendant wields the Aquamarine Dagger in the other hand, on the master’s behalf. This leaves no room to doubt the dagger’s origins; this confrontation in Gael’s boss room was most likely our original means to acquire the weapon before the additional NPC was cut and FromSoftware needed to reimagine its travel history.