Well, loyalty is a big theme. Yamamoto is very loyal to the Soul Society, and fanfics may show how his loyalty affects those around him or how others react to his unwavering loyalty. Also, there's the theme of tradition. He is a big believer in the old ways and traditions of the Soul Society, and fanfics might explore the clashes between his traditional views and the changing times within the Soul Society. Sometimes, there are fanfics that look at how he tries to preserve these traditions against all odds.
One common theme is power. Yamamoto is extremely powerful, and fanfics often explore the extent of his power, like how he can handle really tough enemies. Another theme is leadership. As the head of the Gotei 13, his leadership style and decisions are often the focus. For example, how he manages to keep the Soul Society in order.
In many bleach yamamoto fanfics, the theme of sacrifice is present. Given his position, he might have to sacrifice a lot for the greater good of the Soul Society. This could be sacrificing his own life, relationships, or his principles in certain extreme situations. Another common theme is mentorship. He has a role in guiding the younger shinigamis, and fanfics often show his interactions with them in terms of teaching and mentoring.
Chapter 31 is the strongest chapter-level answer because it starts from Before Shen Lan had reached the backyard, she already heard the sounds of... and follows through on After staying in the study and reading for another day, she finally....
A practical answer is Chapter 99, because it turns the idea into a concrete scene. The chapter opens with Seeing the man approach, one of the individuals with a long scar across..., adds pressure through And so, a ludicrous and chaotic scene unfolded— A tall man wearing..., and ends on Just as she.
The best chapter pointer here is Chapter 36, "The Coldest Variety Show Opening in History". It opens with But soon, people began to question the authenticity of Jiang Li's bare... and closes on After swallowing the food in his mouth, he hurriedly took his megaphone....
Chapter 29 is the strongest chapter-level answer because it starts from Big brother, it's me..." The shadow suddenly spoke and it was Jiang... and follows through on Big brother, are you unwilling?" His mournful expression seemed to signal....
Chapter 33 is the strongest chapter-level answer because it starts from Following the announcement, five artists respectively reposted the Weibo—... and follows through on Although Su Yinwan was considered half a goddess to him, the whole thing....
If you want the clearest chapter reference, go to Chapter 65. Early on, Several minutes later, the room remained silent.; later, the chapter leans on The cameraman then discovered that Jiang Li's door wasn't properly shut,....
The best chapter pointer here is Chapter 66, "This Sister Really Can Hustle!". It opens with I can't take it anymore, why did the young master even find a pair of... and closes on Unable to find a staff member to notify, and not wanting to waste time for....
Chapter 40 is the strongest chapter-level answer because it starts from [Jiang Li claims she copied this herself? and follows through on The handsome guys on this show are so difficult to deal with..
The best chapter pointer here is Chapter 45, "Give a Sweet Date and Then a Slap". It opens with Helplessly, Jiang Yan had no choice but to step on the accelerator. and closes on The guests have to go through so many troubles on the way, while these....
Look to Chapter 89 for the clearest answer. It begins with Director Sun took a step back, "What's the rush?, keeps building through It's true about the go-kart costing one point, but this time we're using..., and lands on If anyone should be mocking her, it should be me.] Wen Jiaojiao stood to....