Discrimination is a key element. Because fish - men faced discrimination from humans, Arlong developed his cruel behavior.
Arlong's back story starts with the general situation of fish - men in the One Piece world. Fish - men are generally stronger than humans underwater. However, they are not treated equally on land. Arlong witnessed the unfair treatment towards his fellow fish - men. He formed his own group and started to act in a rather extreme way. He took over Nami's village as a form of revenge against the humans. Nami, a talented navigator, was forced to be part of his crew in a sense, drawing maps for him in the hope of one day buying back her village's freedom. His actions were a result of the long - standing discrimination that fish - men had endured, but his methods were definitely not the right way to solve the problem.
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.
The key elements in Nakime's back story include her position among the Upper Moons. This gives her a certain level of power and influence within the demon world. Her biwa - playing ability is crucial as it allows her to control the Infinity Castle. This means she can create different areas, barriers, and even manipulate the terrain within the castle. Also, her connection to Muzan is an important aspect. It's likely that Muzan either turned her into a demon or recruited her, and she has remained loyal to him, following his orders in the demon - related affairs.
The key elements are her low - born status, her marriage to a noble, and the tests of loyalty. Her husband tests her in ways like separating her from her children.
In Marth's back story, his identity as a prince of Altea is fundamental. It sets the stage for his future actions. The invasion by Dolhr is a cataclysmic event that upends his life. This leads to his exile, during which he endures hardships and learns valuable skills. His relationships with other characters he meets during this time are also key elements. And of course, his quest to retake Altea and restore order is at the heart of his back story.
The key elements are his poor upbringing, his love for Daisy, and his pursuit of wealth. His early life in poverty drove his ambition. His love for Daisy was the main motivation behind his actions. And his quest for wealth, through whatever means, was to make himself acceptable to her.
His Inazuman heritage is a key element. It's where his family values and traditions come from. The political unrest in Inazuma that led to his leaving is also crucial. And his new life as a wandering samurai, exploring the world and having new experiences, is an important part of his back story as well. He also has his love for poetry which is a unique aspect of his character and is related to his upbringing in Inazuma.
The key elements are his cancer diagnosis, the secret experiment he joined, and his resulting superhuman healing factor.
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 the specific Middy, I can't say for sure. But if Middy was a character in a coming - of - age story, perhaps key elements could be friendship, self - discovery, and facing family issues.