One possibility could be that Sona's brother is a powerful figure in the underworld. He might be involved in political intrigue within the devil society. For example, he could be trying to form alliances with other noble devil families to increase the power and influence of Sona's family. Maybe he has some special abilities that are yet to be discovered by others, which he uses to his advantage in the complex power dynamics of the Highschool DxD world.
In a fanfiction, Sona's brother could be a mentor figure. He might teach Sona some ancient and powerful magic that has been passed down in their family. He could also be a bit of a rebel, going against the traditional ways of the devil society. For instance, he might believe in more equal relationships between devils and other races, like angels or humans, which could cause some conflict within their family and among the other devils.
Perhaps Sona's brother has a tragic past. He could have lost someone he loved dearly in a war between devils and angels. This event could have shaped his personality and goals. He might be on a quest for revenge or trying to find a way to prevent such tragedies from happening again. His relationship with Sona could be complex, as he wants to protect her from the same pain he has endured, but also knows she needs to grow strong in the dangerous world they live in.
Look to Chapter 131 for the clearest answer. It begins with Just around mealtime, Director Sun came over pushing his small food cart., keeps building through There was a loudspeaker tied to the top of the cart, which was..., and lands on Hungry, they no longer cared about their appearance, quickly.
If you want the clearest chapter reference, go to Chapter 170. Early on, Watching the two who had long remained silent, the PD shifted his position...; later, the chapter leans on If you don't set off soon, you'll probably miss lunch." Hearing this, Su....
If you want the clearest chapter reference, go to Chapter 125. Early on, Next, it was Qi Tianyu's turn.; later, the chapter leans on Although he didn't know what Jiang Li had chosen, just from her recent....
Chapter 133 is the strongest chapter-level answer because it starts from Watching Jiang Li and the others finish their meal and tidy up the table,... and follows through on It was only after she shared the concept and purpose of the show with him....
If you want the clearest chapter reference, go to Chapter 151. Early on, Now it was Zhang Cheng's turn to be confused.; later, the chapter leans on The problem lies with He Yun?. By the close, I will have my assistant pay the bill., and the chapter closes with Was he...
Look to Chapter 159 for the clearest answer. It begins with Seeing the red light of the camera turn on, Su Yinwan looked at the..., keeps building through Sorry, director, it was my staff who didn't arrange things well, that's..., and lands on Shang Shaobai, who was browsing through files.
Chapter 125 is the strongest chapter-level answer because it starts from Next, it was Qi Tianyu's turn. and follows through on He deliberately chose the most inconspicuous wheat seeds..
The best chapter pointer here is Chapter 130, "Director Sun: He Got Schooled Again?". It opens with This task, the first one, should have been his in the bag. and closes on Normally, the best planting distance for sweet potato seedlings is 25 to....
If you want the clearest chapter reference, go to Chapter 113. Early on, The next day, Jiang Lili was up before dawn as usual.; later, the chapter leans on But this time was different; as she got dressed and opened her room door,....
A practical answer is Chapter 130, because it turns the idea into a concrete scene. The chapter opens with This task, the first one, should have been his in the bag., adds pressure through Not to mention Wen Jiaojiao, who was still lying in the hospital on an IV..., and ends on Normally, the best.