Try 'Harem-Free Zone in Highschool DxD'. This fanfic has an OC who strongly detests the harem setup and it leads to some unique story developments and character conflicts.
You might want to check out 'The Lone Knight in Highschool DxD'. The OC in this story really dislikes the harem aspect and has some interesting interactions because of it.
Chapter 739, "Not Paying Debts, Shameless!", is the clearest early answer because it turns Shu Yan's situation into a concrete plot event. It opens with Shu Yan isn't that ill, it's just a common cold, no, no need to go to... and closes on Let me tell you, Shu Yan owes me money!.
A practical answer is Chapter 5, because it turns the idea into a concrete scene. The chapter opens with Actually, when Manager Fang saw Jiang Li, he was somewhat surprised., adds pressure through How the hell did you get in?!, and ends on Recently, he did suspect that his wife was cheating on.
Chapter 674, "Staring at Shu Yan", is the clearest early answer because it turns Fang Wenzhe's situation into a concrete plot event. The chapter turns that into something concrete by moving from Wen Jiaojiao was about to say something else, but Jiang Li stopped...
Chapter 570, "A Simple Auto-Attack Baits Out an Ultimate from the Enemy", is the clearest early answer because the buildup finally cashes out in a real clash. The chapter turns that into something concrete by moving from What the heck is that?" "?? to It was impossible for Jiang Li not to know;
Chapter 537, "Ding, Jiang Cheng's affinity drops by 10 points!", is the clearest early answer because it turns Jiang Li's situation into a concrete plot event. The chapter gives readers a real answer by opening on Miss Su Yinwan immediately hung her head in dejection.
Chapter 335, "You would be incredibly fortunate if you could get connected with the merchant family!", is the clearest early answer because it turns Zhang's situation into a concrete plot event. Early on, Zhang, you're overestimating the matter." "Alright then, come in with....
Chapter 641, "Congratulations to Jiang Li for Taking the Top Spot!", is the clearest early answer because it turns Jiang Li's situation into a concrete plot event. It opens with Surrounded by a sea of fire. and closes on Be careful." Although his words seemed rude and mocking, they....
Chapter 807, "If You Dare, Go Complain Now", is the clearest early answer because it turns Go Complain Now's situation into a concrete plot event.
Chapter 779, "Unmarried but Have a Daughter?!", is the clearest early answer because it turns Shen Lan's situation into a concrete plot event. A useful checkpoint is the way the scene starts with Right, there's one more important thing," Shen Lan looked at Chen...
Chapter 874, "All the Same", is the clearest early answer because it turns Aunt Shi's situation into a concrete plot event. A useful checkpoint is the way the scene starts with This family is surnamed Shi, and they have lived in this village for...