Family or lack of it often plays a big role. Maybe his family was killed by criminals, which drove him to become a crime - fighter. This would be a significant part of his back story, as it explains his actions and his alliance with others in the fight against evil.
In the case of Robin Hood, his key back - story element is his opposition to the oppressive regime. He saw the poverty of the people while the rich were living lavishly, so he took action. His skill with a bow and arrow also plays a part in his story as it helped him in his thievery and evasion.
One key element is the character's own sense of justice and courage even before meeting Batman. Then, of course, there's the moment of connection with Batman. It could be Batman seeing the character's potential or the character seeking out Batman's help. Another important part is the character's background which often includes some sort of unique skill set like acrobatics or martial arts training from an early age.
The key element is tragedy. In the case of Dick Grayson, it was the death of his parents. Another element is the mentorship. Batman taking Dick under his wing and training him is crucial. Also, the need for a sidekick in Batman's fight against crime is an important part of Robin's origin.
One key element is his writing. His books are full of inspiring ideas. Another is his speaking skills at seminars. People love to hear him speak.
The destruction of Ohara is crucial. Robin was just a child when it happened. After that, she had to learn to survive on her own. She faced betrayal from people who were afraid to be associated with her. Her decision to keep studying the Poneglyphs despite the danger was also a significant event. And finally, her encounter with the Straw Hat crew and deciding to join them changed her life for the better.
One key element is his origin as a Maia. Another is his association with Morgoth, which shaped his evil nature. Also, the creation of the One Ring is a crucial part of his back story.
The key elements are his cancer diagnosis, the secret experiment he joined, and his resulting superhuman healing factor.
One key element is his fall into the vat of chemicals. It was a turning point that physically and mentally transformed him.
As mentioned before, not knowing the specific Shura makes it hard. But generally, key elements could include their origin, like where they were born. Family might be another, whether they had a loving family or a troubled one.
One key element is his sense of justice. He saw the wrongs done to kids and wanted to fix them.