I'm not sure specifically about 'lemon' fanfiction regarding McGee and Gibbs. Fanfiction can vary greatly in quality and content. You might want to check some popular fanfiction websites like Archive of Our Own and search for McGee and Gibbs stories there. However, keep in mind that 'lemon' usually implies more adult - themed content which may not be suitable for all audiences.
Finding 'lemon' fanfiction can be a bit tricky and also might not be in line with the general ethics of fan communities. Instead of specifically looking for that type of fanfiction about McGee and Gibbs, you could try to find stories that develop their characters in depth. There could be fanfictions that show McGee's growth under Gibbs' guidance or how their different personalities complement each other during investigations.
Look to Chapter 13 for the clearest answer. It begins with Sensing that something was off with Jiang Yan, Jiang Yan dismissed the..., keeps building through What on earth do you mean?" Ignoring him once again, Jiang Li shifted her..., and lands on How could this happen..." Lin Manru didn't want to.
The best chapter pointer here is Chapter 35, "Stunning Beauty Shocks the Prosperous Age, Tops the Trending Searches!!!". It opens with Shining Transformation Trip's filming location was set on the distant... and closes on Brother is really hardworking, actually arriving at the same time as the....
The best chapter pointer here is Chapter 17, "Madam, the eldest young master has disappeared again". It opens with Jiang Li glanced at Jiang Shixu, who was tense and anxious behind her, and... and closes on I've been a mother for more than ten years but never tasted anything made....
Chapter 52 is the strongest chapter-level answer because it starts from The village chief and the woman behind him exchanged a glance, "This... and follows through on And at this point, they might as well try a desperate remedy for a....
The best chapter pointer here is Chapter 34, "Official Recording!". It opens with Seeing that the public sentiment wasn't quite right, Su Yinwan felt... and closes on Now that Lili is misunderstood, they start to kick us while we're down."....
The best chapter pointer here is Chapter 14, "She Looks So Cool Dancing with a Gun". It opens with Lin Manru had a rare good night's sleep. and closes on But clearly, Lin Manru was unable to accept that her delicate daughter had....
Chapter 11 is the strongest chapter-level answer because it starts from After a meeting, Shang Shaojing pinched the bridge of his nose, tired, and... and follows through on Miss Qin, please accompany us to the police station to explain this....
A practical answer is Chapter 31, because it turns the idea into a concrete scene. The chapter opens with Before Shen Lan had reached the backyard, she already heard the sounds of..., adds pressure through And judging from the photo, she was also a stunning natural beauty!, and ends on After.
The best chapter pointer here is Chapter 5, "Catching Adultery Personally". It opens with Actually, when Manager Fang saw Jiang Li, he was somewhat surprised. and closes on Recently, he did suspect that his wife was cheating on him, but due to the....
Chapter 16 is the strongest chapter-level answer because it starts from Just as the words fell, Jiang Shixu swiftly cast his eyes downward. and follows through on Jiang Shixu panicked, set down the bowl, and reached forward to grab her....