For Grey's Anatomy, the 'medical mystery' trope is a staple. In X - Men, the 'discovery of new powers' trope is popular. Fanfiction could merge these by having a character in Grey's Anatomy suddenly start exhibiting strange symptoms that turn out to be the emergence of mutant powers. The doctors then have to figure out not only how to stop any negative effects but also understand what these new powers are and how they can be controlled.
In Grey's Anatomy fanfiction, the 'forbidden love' trope is quite popular. This could be between two doctors who are in different positions in the hospital hierarchy or have some other obstacle to their relationship. In X - Men fanfiction, the 'outsider' trope is common. New mutants coming into the X - Men group and feeling like they don't belong at first. When combined, you might have a story where a Grey's Anatomy character who is an outsider in the hospital (maybe a new intern) discovers they are a mutant and feels like an outsider in both worlds.
The 'redemption' trope works well for both. In Grey's Anatomy, a doctor who has made a big mistake tries to make up for it. In X - Men, a former villain mutant tries to redeem themselves. A fanfiction could be about a character from Grey's Anatomy who has a dark past (like accidentally causing a patient's death) and then discovers they are a mutant and uses their new powers to try and redeem themselves in the eyes of both the medical community and the mutant community.
A practical answer is Chapter 92, because it turns the idea into a concrete scene. The chapter opens with Jiang Li, lightened from any task, had plucked a few leaves from the..., adds pressure through Just as Jiang Li was about to refocus and continue expanding her..., and ends on Finally, someone.
A practical answer is Chapter 116, because it turns the idea into a concrete scene. The chapter opens with But before the audience in the live room had time to continue brewing the..., adds pressure through So, he quickly nodded as if pounding garlic, "That would trouble Sister Li..., and ends on.
The best chapter pointer here is Chapter 67, "You Can Still Pick Mushrooms?!". It opens with I'm pissed," Jiang Yan cursed again, "These people are too much, aren't... and closes on Accompanied by the wisps of smoke gradually rising from the stove behind....
If you want the clearest chapter reference, go to Chapter 115. Early on, Jiang Yan was woken by a loud crowing noise.; later, the chapter leans on Annoyed, he opened his eyes and saw that the hen, which should have been....
Look to Chapter 110 for the clearest answer. It begins with Jiang Li, carrying a wooden basin, walked over to the well., keeps building through Uncle Zhao's house didn't have a water heater, so she could only make do..., and lands on My parents died, and fortunately, Daddy found and took me in..
Chapter 95 is the strongest chapter-level answer because it starts from Hearing others praise her daughter, Aunt Lin was smiling so wide she... and follows through on Your boyfriend must have studied in another province, if I'm not mistaken,....
Chapter 77 is the strongest chapter-level answer because it starts from Wen Jiaojiao's reminder calmed Shu Yan down. and follows through on But who knew that the next second, the lottery box would be handed over to....
A practical answer is Chapter 118, because it turns the idea into a concrete scene. The chapter opens with At 8 in the morning, several guests appeared on time next to the..., adds pressure through How can I see what you're saying?, and ends on Hearing this, both Jiang Yan and Shu Yan started to.
If you want the clearest chapter reference, go to Chapter 107. Early on, On the plane, when He Yun had taken off his mask and greeted her...; later, the chapter leans on She had also figured out his current predicament of being trapped by....
A practical answer is Chapter 79, because it turns the idea into a concrete scene. The chapter opens with Jiang Li leisurely said, "I bought this weeding machine, and according to..., adds pressure through Many had even spontaneously formed a fan group for Jiang Yan, promoting..., and ends on.