Rite of Rebirth

The Rite of Rebirth was ritual created by the god Bahamut designed to transform good-aligned non-draconic humanoids into dragonborn.

Background
The Platinum Dragon rejected the thought of breeding creatures to oppose the aberrant creations of Tiamat. He instead sought out humanoid volunteers of any non-draconic race who had shown strong determination and the will to work against vile draconic creatures. A potential recruit's past didn't matter to Bahamut while the candidate had demonstrated the commitment to oppose Tiamat and her spawn. Even wrongdoers found redemption and purpose in becoming Bahamut's servants.

Usually, Bahamut called those humanoids he had chosen before adolescence, but sometimes adults heard the call of the Platinum Dragon as well. The call was a courteous mental question, asking in the hearts and souls of those deemed worthy if were willing to undertake the duty to protect the world from the spawn of Tiamat, giving up all that they were until that moment of their lives for a life of hardships and sacrifices. Not all those who were called answered, but those who did it underwent a magical process known as the Rite of Rebirth.

Those who committed to this demanding ritual meditated for a full day and night, their head filled with reminders of all they were giving up. Those who elected to go on, prepared a specially-built egg-shaped chamber and entered it to sleep for another full day and night, emerging the next dawn as an adult dragonborn (regardless of their previous age), a draconic humanoid with metallic scales and draconic abilities. They had been reborn as permanent champions of the Platinum Dragon.

History
The Rite of Rebirth was created during the Time of Dragons, when Bahamut first sought out volunteers to become dragonborn and help him battle the spawn of Tiamat. The knowledge of the ritual resurfaced in 1359 DR, when Bahamut regained his deific status and began to search once more for those worthy of being called his children.

After the last Rage of Dragons, in 1373 DR, many non-dragon devotees of Bahamut began to feel a strong urge to become dragonborn. Many of those who were called underwent the Rite of Rebirth, and the Sisterhood of Essembra helped those who were interested in taking the rituals and sought their help.