There are many entities that could be considered main characters. For example, the various SCPs like SCP - 173 and SCP - 096. These entities play a major role in the horror and mystery aspects of the story.
The Foundation personnel are also main characters in a way. They are the ones who try to contain and study these SCPs. Without them, there would be no story as they are the ones facing the challenges posed by the SCPs. They have different roles within the Foundation, from researchers trying to understand the SCPs to security personnel trying to keep them contained.
Another important group could be the D - Class personnel. These are the expendable individuals used by the Foundation for various tests involving the SCPs. Their experiences and fates within the SCP Secret Files Story add a lot to the overall narrative, showing the darker side of the Foundation's operations as they are often put in extremely dangerous and unethical situations.
Chapter 858, "If You Dare, Take It", is the clearest early answer because it turns Jiang Li's situation into a concrete plot event. It opens with Changqing flicked his horsetail whisk, face wooden, and said,... and closes on When is it going to be completed so I can visit?] [Whoa, it's....
Look to Chapter 21 for the clearest answer. It begins with Jiang Li's clear and logical explanation had everyone stunned in place., keeps building through Jiang Yan had wanted to defend Su Yinwan since his sister's temper in the..., and lands on But the implications could be different..
Chapter 748, "Blacklisted", is the clearest early answer because it turns Blacklisted Jiang Li's situation into a concrete plot event. Early on, Jiang Li certainly wouldn't pass up the opportunity of having a.... By the end, The big competition is in just a few days, and I can't sleep." "Don't....
Look to Chapter 16 for the clearest answer. It begins with Just as the words fell, Jiang Shixu swiftly cast his eyes downward., keeps building through His eyelashes were very long;
Look to Chapter 43 for the clearest answer. It begins with The moment He Yun willingly sat next to Jiang Li and even took off his..., keeps building through Movie Emperor He, where's your aloof persona?" "Waaah, He Bao, Mommy..., and lands on Just as she turned her gaze away, the other party.
Chapter 710, "Handsome, Who Are You?", is the clearest early answer because it turns Handsome's situation into a concrete plot event.
If you want the clearest chapter reference, go to Chapter 2. Early on, On the top floor of the Financial Building, a gathering of dark clouds...; later, the chapter leans on How dare Jiang Li hang up his phone?.
If you want the clearest chapter reference, go to Chapter 4. Early on, Qiao regretted her words as soon as they left her mouth.; later, the chapter leans on Whether Jiang Yan can be found or not was another matter..
Chapter 18 is the strongest chapter-level answer because it starts from In the corner, a girl in a black dress sat quietly, holding a glass of... and follows through on Hurry home, what is a young lady like you doing running to a place like....
Chapter 875, "Isn't That Xu Mei's View?", is the clearest early answer because it turns Jiang Bufan's situation into a concrete plot event. The chapter turns that into something concrete by moving from In the information network of the three people, Lu Yafei and Wan Jia...