I'm not sure where you can specifically find a 'Black Bullet' fanfic about Rentaro and Kisara with 'lemon' content (which often implies adult or inappropriate themes). Fanfics with inappropriate content are not allowed on many official platforms. You could try looking on general fanfic websites but be aware of their terms of use.
Finding fanfics with 'lemon' content is not advisable as it goes against the rules of many platforms. However, if you're looking for regular, appropriate fanfics about Rentaro and Kisara from 'Black Bullet', you can check out websites like Archive of Our Own. They have a large collection of fanfics, but they strictly regulate inappropriate content.
If you want the clearest chapter reference, go to Chapter 133. Early on, Watching Jiang Li and the others finish their meal and tidy up the table,...; later, the chapter leans on But when he went to the firewood shed to find a convenient wooden tub, he....
If you want the clearest chapter reference, go to Chapter 120. Early on, Facing the sudden and somewhat strange request from Jiang Li, Director Sun...; later, the chapter leans on But, as if by some mysterious force, he still instructed his assistant to....
If you want the clearest chapter reference, go to Chapter 152. Early on, While most of the villagers of Chixia Village were gathered at the village...; later, the chapter leans on The unassuming structure stood out oddly against the backdrop of its....
A practical answer is Chapter 165, because it turns the idea into a concrete scene. The chapter opens with How come everyone else got a solid six points, and he ended up with just..., adds pressure through And this scene was fully witnessed by Zhao Lang from the second floor., and ends on Various.
Look to Chapter 157 for the clearest answer. It begins with It was already the last day of Flash Change in his dream., keeps building through His good score had successfully surpassed Jiang Li, making him first in..., and lands on I'm laughing myself crazy, do actors all have such strong.
The best chapter pointer here is Chapter 157, ""Forced onto Liangshan". It opens with It was already the last day of Flash Change in his dream. and closes on I'm laughing myself crazy, do actors all have such strong conviction?]....
If you want the clearest chapter reference, go to Chapter 129. Early on, When they saw that the live chat was full of praise for Jiang Li, those...; later, the chapter leans on Had they been used as pawns by publicity accounts?!.
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 138 is the strongest chapter-level answer because it starts from Is there such a good deal? and follows through on Could it be that the poison also had a side effect of making a person more....
If you want the clearest chapter reference, go to Chapter 136. Early on, A few people retraced their steps back to the place they had just been.; later, the chapter leans on They continued straight up the mountain path until the trees became denser....