The plot is a major factor. A story that has an interesting backstory leading up to the kiss, like they have to overcome some challenges together or they have a misunderstanding that needs to be resolved first. Also, the way the kiss is described can make it popular. If it's written in a very emotional and detailed way, it can draw in readers.
Popularity can also come from how the fanfiction fits into the overall 'Wild Kratts' universe. If it references other characters in a meaningful way, or if it adds something new to the existing relationships in the show. For instance, how their kiss might affect their relationships with the other Kratt brothers or the villains in the show. Additionally, the writing style matters. A clear, engaging writing style with good grammar and pacing will make more people want to read the story.
Chapter 874, "All the Same", is the clearest early answer because it turns Jiang Li's situation into a concrete plot event.
If you want the clearest chapter reference, go to Chapter 33. Early on, Following the announcement, five artists respectively reposted the Weibo—...; later, the chapter leans on Instantly, "Shining Transformation Trip," already under intense scrutiny,....
If you want the clearest chapter reference, go to Chapter 28. Early on, The next evening, Jiang Yan drove home seething with rage.; later, the chapter leans on Before he even entered the dining room, he shouted angrily, "Lili, you did....
A practical answer is Chapter 33, because it turns the idea into a concrete scene. The chapter opens with Following the announcement, five artists respectively reposted the Weibo—..., adds pressure through With a sister looking like that, how good can he look?], and ends on Although Su Yinwan was.
Chapter 926, "Doomsday Beehive Exploded?!", is the clearest early answer because it turns Jiang Bufan's situation into a concrete plot event. A useful checkpoint is the way the scene starts with What's this?" Zhao Lang looked at the unimpressive box in his hand...
If you want the clearest chapter reference, go to Chapter 19. Early on, What criminal law is this or that, this was originally none of your...; later, the chapter leans on In high school, she got into the international class by throwing money....
A practical answer is Chapter 25, because it turns the idea into a concrete scene. The chapter opens with Therefore, from his childhood, Jiang Shixu had felt an extreme aversion to..., adds pressure through When she saw the woman behind the desk, she smiled and said, "Look who..., and ends on.
Chapter 25 is the strongest chapter-level answer because it starts from Therefore, from his childhood, Jiang Shixu had felt an extreme aversion to... and follows through on Having worked beside Shen Lan for over a decade, she had been there when....
Look to Chapter 4 for the clearest answer. It begins with Qiao regretted her words as soon as they left her mouth., keeps building through Whether Jiang Yan can be found or not was another matter., and lands on A little girl acting mysterious, learning fortune-telling, what is this....
Chapter 867, "Then what does our child count as?!", is the clearest early answer because it turns Watching Jiang Meng's situation into a concrete plot event. The chapter gives readers a real answer by opening on Lili's brother, Chen Nanyu, was the only ray of light in his dark...