Thinking back, Ranko was probably aware that Usogui acquired the L-file since Ranko and Kaji met at Hayama's house during the Mechnical Bull gamble. So perhaps at that point on, Ranko devised the plan to overtake Usogui here, knowing he'd use the L-file to gain lots of money and power for the leader gamble.
Also in that gamble, Kakerou wasn't called, so they aren't aware of that chance meeting. This might be why Yakou suspected Suteguma to be from Ideal, since only Ideal should be aware that Usogui has the L-file (Outside of the police and Kakerou).