The experiment happens after the first stage of the tournament, but if I remember correctly, she actually asks you to do it when He Gang returns. You have to go ask her for advice about your cousins when He Gang says he killed them or something like that—I don’t remember exactly. It’s the scene where He Gang throws acid at you, I think, and you tell Mei Mei about Qi and all that. That event leads to the experiments later on.What does it take to trigger the experimentation? In my runs either the MC escapes the cave if he fails to convince her or ends up in a confirmed partnership if he does. The former you are enemies from that point forward because she chained you up and latter you are working together.
As for the part you mentioned about the confirmed partnership relation, I’m guessing you didn’t confess your feelings to Mei? At least in my route I did, so I’m on her romantic route—or at least what seems to be it—not the business one, so I’m not sure if it’s the same.

