Since it's about Sonic, Sonic himself is most likely a main character. There might also be his friends like Tails and Knuckles who would be involved in the story.
In a 'dark sonic flash story', Sonic is surely a main character. Given the nature of the story being dark, there could be some new or antagonist characters as well. But Sonic's friends such as Tails, who is his loyal sidekick with his intelligence and mechanical skills, and Knuckles, the strong guardian of the Master Emerald, would probably play important roles too. They would be there to either help Sonic if he's in trouble or try to stop him if he goes too far in his 'dark' state.
The main character is bound to be Sonic in the 'dark sonic flash story'. However, depending on how the story is crafted, other characters could be crucial. Tails, with his ability to build and repair things, would be a great asset in the story. Knuckles, with his strength and connection to the Emeralds, would also be a key figure. And there could be a villain, perhaps an evil wizard or a powerful mechanical being that has the power to corrupt Sonic and set off this 'dark sonic' scenario.
Look to Chapter 115 for the clearest answer. It begins with Jiang Yan was woken by a loud crowing noise., keeps building through Annoyed, he opened his eyes and saw that the hen, which should have been..., and lands on [Pure bystander, wasn't Jiang Yan known as a notorious playboy?.
The best chapter pointer here is Chapter 117, "What Jiang Li Can Do, She Can Do Too!". It opens with Fragrant and cloyingly sweet potatoes and corn were out of the pot, and Qi... and closes on Since entering puberty, his mother had exerted strict control over his....
If you want the clearest chapter reference, go to Chapter 102. Early on, When the camera cut back, the three of them had already returned to the...; later, the chapter leans on The mud on Jiang Yan's body had dried mostly from the wind, and he walked....
A practical answer is Chapter 122, because it turns the idea into a concrete scene. The chapter opens with Damn, are we supposed to find the points card in the mud?!" He had just..., adds pressure through It wasn't intentional!" Bullet screen: "[Qi Tianyu, you really need to be..., and ends on He.
If you want the clearest chapter reference, go to Chapter 105. Early on, But this did not elicit any sympathy from the woman on the phone; on the...; later, the chapter leans on Do you know why you haven't been getting good roles or making money these....
A practical answer is Chapter 131, because it turns the idea into a concrete scene. The chapter opens with Just around mealtime, Director Sun came over pushing his small food cart., adds pressure through Just as they tried to emulate Jiang Li's example and make themselves a..., and ends on Hungry.
Chapter 103 is the strongest chapter-level answer because it starts from Jiang Yan looked at Zhao Lang with suspicion, eyeing the dark substance in... and follows through on Jiang Yan felt deep guilt welling up inside him..
If you want the clearest chapter reference, go to Chapter 100. Early on, The barrage was about to die of laughter.; later, the chapter leans on [Hahahaha, help, why is the young master always being chased!] [Next door,....
The best chapter pointer here is Chapter 103, "Selling a Kidney to Repay Debt". It opens with Jiang Yan looked at Zhao Lang with suspicion, eyeing the dark substance in... and closes on Jiang Yan felt deep guilt welling up inside him..
If you want the clearest chapter reference, go to Chapter 112. Early on, These five people are supposed to be at odds.; later, the chapter leans on When did they become so in sync?] [I'm dying of laughter hahaha why is....