Another important element is his exposure to the unfairness between kids and adults. This motivated him to take action and form the Kids Next Door, which is central to his back story.
One key element is his sense of justice. He saw the wrongs done to kids and wanted to fix them.
One key element is his upbringing in a wealthy family which allowed him to pursue his passion for hunting. Another is his boredom with normal hunting and his consequent search for a more challenging quarry, which led him to Spider - Man. Also, his sense of self - importance and the need to prove himself as the greatest hunter are important parts of his back story.
One key element is his thirst for strong opponents. It's what drives him in the story.
One key element is the influence of different musical styles. As I mentioned before, it draws from rock, R&B, etc. Another is the role of media. Radio and later TV were crucial in making pop music popular. For example, shows like American Bandstand introduced new pop acts to a large audience.
One key element is his scientific genius. It's what got him into all the multiverse adventures. Another is his family. His relationship with his daughter and the loss he experienced within his family are major parts. Also, his recklessness in his experiments which led to so many consequences both good and bad in his life.
One key element is her origin in Zaun. It's a place that shaped her. Another is her mental instability which grew over time. Also, her exposure to the rough and chaotic environment of Zaun is important.
As I don't know which Kino it is, I can't say for sure. But usually, key elements in a back story could be things like a major event that changed their life, like the loss of a loved one.
In Venom's back story, the key elements include the origin of the alien symbiote from outer space. This symbiote has unique biological properties that give Venom its abilities. Eddie Brock's personal history is also important. His fall from grace as a journalist and his resentment towards Spider - Man made him a perfect candidate for the symbiote. Moreover, the symbiote's brief stint with Spider - Man is a key element. It was during this time that the symbiote learned about Earth and its potential hosts, which ultimately led to its union with Eddie Brock and the creation of Venom.
One key element is his Atlanta upbringing. The city's street culture influenced him. Another is poverty, which was a big part of his early life.
One key element is his origin on Titan. Another is the overpopulation and resource scarcity he witnessed there. And of course, his obsession with the Infinity Stones to carry out his plan of wiping out half of all life.
The key elements in Rossi's back story may include his relationships. Maybe he had a special friendship or a rivalry that had a big impact on him. Also, his career choices and how he got into them. For instance, if he's a chef, what made him choose that path? Was it a family tradition or his own passion? His early experiences in the kitchen, like learning from his grandmother or working in a local diner, could be part of it.