Well, the appeal might lie in the contrast between the characters. Naruto is an energetic and determined ninja, while Batgirl is a strong, intelligent crime - fighter. Their different personalities and abilities can create a lot of interesting dynamics in a romantic relationship. Also, fans like to explore how two characters from different fictional realms would interact and fall in love, which gives a lot of room for creativity in fanfiction.
Chapter 942, "In Which Year Did the River Moon First Shine on People [Extra · River Moon Edition]", is the clearest early answer because it turns Shu Yue's situation into a concrete plot event. It opens with She never expected Jiang Yan meant this. and closes on That was definitely not a dream!.
Chapter 509, "Don't Cry Funeral Until Someone Dies", is the clearest early answer because it turns Jiang Li's situation into a concrete plot event. A useful checkpoint is the way the scene starts with Because of the commotion from the night before, Jiang Li had...
Chapter 605, "The Plan to Surround and Annihilate Team Q Commences!", is the clearest early answer because it turns Shang Shaojing's situation into a concrete plot event.
Chapter 531, "She Really is a Remarkable Person", is the clearest early answer because it turns Zhou Xu's situation into a concrete plot event. The chapter turns that into something concrete by moving from Zhou Xu also brought over a plate of sunflower seeds and was just...
Chapter 534, "This Grand Era is as You Wish", is the clearest early answer because it turns Team's situation into a concrete plot event. The chapter turns that into something concrete by moving from Pei Ye swiftly tossed all those people far away.
Chapter 819, "Invitation", is the clearest early answer because it turns Jiang Yan's situation into a concrete plot event. The chapter turns that into something concrete by moving from What Yu Li said is something these prominent families often do. to Lin Manru's studio also resumed work..
Chapter 514, "Truly Deserved! Number One on the Individual Ranking!", is the clearest early answer because it turns Zhou Wenqi's situation into a concrete plot event.
Chapter 832, "So Impressive, My Sister!", is the clearest early answer because it turns Wen Jiaojiao's situation into a concrete plot event.
Chapter 755, "You didn't fail to receive the invitation, did you?", is the clearest early answer because it turns Jiang Cheng's situation into a concrete plot event. Early on, Shu Yan hadn't expected to earn so much even before she started her....
Chapter 745, "I'm Pregnant", is the clearest early answer because it turns Jiang Li's situation into a concrete plot event. The chapter turns that into something concrete by moving from Several people finally met Shu Yan in the hospital ward.