Start by showing his initial goals and motives clearly. For example, if his goal is to conquer a certain planet, show his determination and the lengths he will go to achieve it.
Well, in fanfiction, if Goku Black fuses with Goku, it could result in a super powerful being. Their combined powers might create a new form with an extremely high power level. This new entity could have a mix of Goku Black's dark and devious nature with Goku's pure-hearted heroism, leading to an internal struggle within the fused form.
If Goku Black fuses with Goku in fanfiction, the story would progress in a complex way. The fused form might go on a journey to understand itself. Since it has two very different personalities combined, it would face a lot of internal conflict. This could be used to explore themes like identity and the struggle between good and evil. Externally, the fused Goku could attract new enemies who see it as a threat to their power or plans.
Joan didn't turn dark. Joan of Arc was a national hero of France. She led the French army against the invasion of the British army in the Hundred Years 'War and was eventually captured and burned by the British army. Joan of Arc was widely portrayed as a symbol of purity, courage, and loyalty, and her story was adapted into many literary, film, and dramatic works. Blackening was a term that was used to describe a person's character or behavior that had undergone an extreme change, from kindness and integrity to evil and cruelty. Joan's image was that of a staunch Christian believer. Her actions and words were based on her beliefs and moral principles. Although her actions and words were sometimes surprising, they were all out of her loyalty and love for France and Buddhism. Therefore, Joan of Arc was not corrupted. Her image was a symbol of determination, courage, loyalty, and purity.
While waiting for the TV series, you can also click on the link below to read the classic original work of "Dafeng Nightwatchman"!
Another characteristic is the expansion of the Goku Black universe. It could introduce new powers for Goku Black, or new versions of the characters he interacts with. For instance, a fanfiction might give him a new transformation that is unique to that story. The best Goku Black fanfictions also manage to stay true to the essence of his character while still bringing something new and exciting to the table.
Asta's age in the Black Clover story arc changes over time. At the beginning, he's around 15 years old, and as the story goes on, he gets older. The exact age depends on the particular events and chapters.