Celestia is often paired with King Sombra. Their power levels are somewhat similar, and they represent opposite sides of good and evil, so it makes for an interesting dynamic. Twilight Sparkle is also a common character to be paired with him. Given Twilight's knowledge of magic, she could either be in a battle of wits with Sombra or trying to understand his magic for some reason.
Fluttershy might be paired with King Sombra in some fanfictions. The contrast between her gentle nature and his dark, menacing presence can create a really unique story. She could be the one to approach him and try to tame his dark side. Another character is Discord. Since Discord is also a being of chaos, his interactions with King Sombra, who is a symbol of darkness, can lead to all sorts of wild and unpredictable plots.
Princess Luna could be paired with King Sombra. Luna has her own past with darkness, having once been Nightmare Moon. So she might be able to relate to Sombra in some ways. Their meetings could be about her trying to convince him to turn away from his evil ways, or they could be in a power struggle where they both have different ideas about how to rule the dark elements in Equestria.
Look to Chapter 53 for the clearest answer. It begins with Night had fallen over Chixia Village, eerily void of any human sounds., keeps building through Jiang Li followed the village chief's wife down a narrow path leading to..., and lands on Wait, did this kid accidentally fall into the water?].
If you want the clearest chapter reference, go to Chapter 73. Early on, Director Sun, tongue-tied, finally managed to squeeze out a sentence,...; later, the chapter leans on But isn't it due to your production team's lack of consideration?.
Chapter 117 is the strongest chapter-level answer because it starts from Fragrant and cloyingly sweet potatoes and corn were out of the pot, and Qi... and follows through on Since entering puberty, his mother had exerted strict control over his....
The best chapter pointer here is Chapter 106, "The Beginning of the Butterfly Effect". It opens with Thinking of this, He Yun nodded with a hint of anticipation. and closes on Jiang Li's fingers lingered over the three copper coins, her clear voice....
A practical answer is Chapter 111, because it turns the idea into a concrete scene. The chapter opens with The main room's door was pushed open just a crack, and the head of the..., adds pressure through Alright, those who think they're the king can step forward!" As soon as he..., and ends on.
The best chapter pointer here is Chapter 83, "Can Actually Carve Flowers?!". It opens with When they received the task, the three of them were already sharpening... and closes on Since all the guests were staying at Uncle Zhao's cabin, Director Sun....
The best chapter pointer here is Chapter 74, "Ordinary People". It opens with Having seen Jiang Li's ID before, he knew that this person named Shiguang... and closes on The man's phoenix eyes narrowed slightly, he looked at the girl sitting....
Chapter 129 is the strongest chapter-level answer because it starts from When they saw that the live chat was full of praise for Jiang Li, those... and follows through on With that thought, he smugly turned on his phone..
A practical answer is Chapter 86, because it turns the idea into a concrete scene. The chapter opens with After over an hour of fuss, it was finally time to eat., adds pressure through Having tasted the tomato and eggs again, Wen Jiaojiao sighed in relief,..., and ends on But then her expression.
A practical answer is Chapter 124, because it turns the idea into a concrete scene. The chapter opens with Since there were too many points cards inside Jiang Li's barrel, Director..., adds pressure through Always so impolite to Director Sun, that's a bit too much.], and ends on No need to repeat.