Argon Coin

is the pelt of the golden winged ram Chrysomallos, given to of by as a token of his gratitude. It was possessed by Medea, the princess of Colchis, and she was made to blindly love Jason, who was sent to Colchis to retrieve it, by the goddess Aphrodite in order to defeat King Aeëtes. She nullified her father's magic, allowing Jason to obtain it. It is inhabited by a strange Guardian Spirit, similarly to the Seventh Holy Scripture.
 Caster does not possess it as an active or sealed Noble Phantasm, but instead as a Skill. Jason also has a Skill that shows proof that he obtained The Sought-After Golden Fleece.
It is very valuable as the hidden treasure of Colchis, and while there is nothing special about the fleece itself, there is an anecdote that a dragon will appear if it is thrown on the ground. The exact reason isn't known, but it seems people have mixed up the Golden Fleece with the dragon that used to guard it, making the story feel like some kind of satire. While it is capable of summoning the original that guarded it, Caster does not have the knowledge or skill to summon a Phantasmal Beast, so it goes unused during the Fifth Holy Grail War. If she did possess the proper skills necessary to summon the dragon, it would bring her up from being the weakest Servant to the middle ranking among the Servants of the Fifth War. However, the dragon itself isn't strong enough to be able to make a clear difference against higher level opponents.
This Noble Phantasm is the reason that Atrum Galliasta chose to summon Medea, because he wanted a dragon.Lord El-Melloi II Case Files Volume 3: case. Twin Towers of Iselma (Lower) - Epilogue
==Development==
The spirit's gender is not set in stone, and was originally supposed to appear in Fate/stay night. Gilgamesh was placed into the story instead, and any involvement with Argon Coin was forgotten. It was only referenced in Fate/side material because they were searching for material to put in its encyclopedia. It was going to be in Fate/hollow ataraxia, but that ended up not coming to fruition. It was given some rough art designs in Fate/complete material V, where it is shown having a bad relationship with Caster.
==References==
it:Argon Coin
Category:Noble Phantasms
Category:Unclassified Noble Phantasms
Category:Unknown rank Noble Phantasms
Category:Noble Phantasms introduced in Fate/stay night
Category:Summon Noble Phantasms
Category:Noble Phantasms of the Argonauts