Since we don't have much information about this specific fanfic, it's difficult to say for sure who the other main characters are. However, in a punishment - game - themed fanfic, there might be Kaoru's friends or rivals involved. Maybe there's a group of characters who are all participating in the game together, and they could be classmates, club members, or just friends in the story's universe.
In this 'Hi Kaoru Punishment Game Lemon Fanfic', apart from Kaoru, there could be characters who are related to the setting of the punishment game. For example, if the game takes place in a school, there might be teachers or other students. If it's in a club setting, then fellow club members would be likely candidates for main characters. Also, there could be a love interest for Kaoru, which might play an important role in the story, especially considering the 'lemon' aspect which could imply some sort of romantic plotline.
The best chapter pointer here is Chapter 11, "She Smiled, He Panicked". It opens with After a meeting, Shang Shaojing pinched the bridge of his nose, tired, and... and closes on Miss Qin, please accompany us to the police station to explain this....
Chapter 682, "Too Conspicuous to Keep Around", is the clearest early answer because it turns Chen's situation into a concrete plot event. The chapter turns that into something concrete by moving from Taking advantage of the still-open elevator doors, Su Yinwan quickly...
Chapter 553, "His Love Runs Deep", 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 His gaze shifted to Luo Xuan's empty hands, and Ai Xiaochun's...
Chapter 892, "Richard?!", is the clearest early answer because it turns Zhao Lang's situation into a concrete plot event. The chapter turns that into something concrete by moving from Zhao Lang really wanted to tell Jiang Yan the truth. to Don't go!" Zhao Lang helplessly pried his hand away..
Chapter 452, "Party of Four", is the clearest early answer because it turns Shang Shuyue's situation into a concrete plot event. It opens with Shang Shuyue glared at Jiang Yan, struggling to find the words to say. and closes on Who could blame her when Jiang Li cooked even better than her mom?.
Chapter 836, "It's been a long time since I last saw Jin Siyue", is the clearest early answer because it turns Shi Lei's situation into a concrete plot event. The chapter turns that into something concrete by moving from You!" Rong Junsheng seemed to have heard the commotion over here and...
Chapter 577, "Cat and Mouse Game", is the clearest early answer because it turns Jiang Yan's situation into a concrete plot event.
Chapter 816, "Don't Take Them Seriously", is the clearest early answer because it turns Lin Manru's situation into a concrete plot event. The chapter gives readers a real answer by opening on Unexpectedly, they didn't cry or fuss; they stopped right by Meng...
Chapter 795, "Trouble Befalls the Third Lady!", is the clearest early answer because it turns Lin Manru's situation into a concrete plot event.
Chapter 716, "Cook a Special Meal", is the clearest early answer because it turns Cook's situation into a concrete plot event. The chapter gives readers a real answer by opening on The following week was much quieter, and Jiang Li finally had some...