This was also my introduction to kyonshi/jiangshiI've trained my whole life for this moment
He explained it when he got the thing from the cursed trunk, he needs them to acknowledge that he beat them, and then he stabs to take their powers. He got Takakura to admit he won, and drew the knife, but there were no powers to take, so he didn't stab. He may have also been distracted by the innocent smile of "wow, you sure know a lot of trivia" he got.I might be wrong here (It's Dandadan, super hard to predict) but I don't think the person who put Kouki up to it is St. Germaine. Since he tried to take Ken's powers with the same thing and didn't try to stab him with it. I would like to think he is just a chill guy. (Besides trying to take kens powers)
I have another theory. I think that the defeat admission must be genuine and heartfelt, otherwise the power steal doesn't work. Okarun was in a rush and trying to get rid of him, so he just followed along his words without real meaning behind them.He explained it when he got the thing from the cursed trunk, he needs them to acknowledge that he beat them, and then he stabs to take their powers. He got Takakura to admit he won, and drew the knife, but there were no powers to take, so he didn't stab. He may have also been distracted by the innocent smile of "wow, you sure know a lot of trivia" he got.
The card guy was insincere, thinking he would get away after, but he did admit he lost and that was all that mattered.I have another theory. I think that the defeat admission must be genuine and heartfelt, otherwise the power steal doesn't work. Okarun was in a rush and trying to get rid of him, so he just followed along his words without real meaning behind them.