The Nameless Dragon is the dragon that forms the Dragon Sword of Ryu Himora II from Draconia. Little is known about this dragon; confirmed facts include that she is a female gold dragon, is older than the history of the current Order of the Dragons, and that only a handful of people know her real name. She has apparently told Ryu Himora II her name, but he refuses to share it until she says otherwise.
Ryu Himora II found his Dragon Sword while escaping from a Starbringer facility when we was 12 years old - this is likely the reason why no other dragon has any information on her. By the time of Invasion, her sword form was that of a short medieval European blade with a somewhat ornate handle, leading to some slightly awkward moments as Ryu was expecting a longer blade. Afterward, she decided to take the form of a more standard 1 meter katana with a golden handguard and plain two-hand handle; this has been her default form ever since. Other weapons she has taken the form of inculde a scimitar, scythe, a length of lead pipe, an aluminium bar, a handgun, and a crossbow.
During a mission where she was apart from Ryu, she was referred to as Alpha 2.
Due to her age, the Nameless Dragon has never been shown or described in her dragon form - Ryu says she is a gold dragon, and it is likely that she simply told him this, but it is possible that nobody knows for sure. She has appeared in human form several times, a pale white form with short blonde hair and gold eyes.
The Nameless Dragon's exact age is up for debate, however she is almost certainly the oldest dragon still alive, since she has memories of the the Draconic Schism War. This means she is older than both Bahamut and Tiamat, as both of them were born after the war, and they both lament the fact that they have watched several generations of their people die out.
Since the fate of Xylomeru is not known, it is possible that she is the Nameless Dragon, as the two share several traits - they are both female gold dragons who have very good relationships with humans, do not think much of taking human form themselves, and both apparently hold many secrets. Her military codename, Alpha 2, is also a link to Xylomeru, who was the second mortal dragon ever born. If the Nameless Dragon is Xylomeru, then she most certainly knows the location of the Divine Egg and what, if anything, has hatched from it.