When Sonoko invited Ran, Kogoro, Conan and Sera to attend a foods show with her. They stumbled on a murder. Eventually Sera and Conan solved the mystery, figuring out the trick used. Conan and Ran found Sera too familiar and realized they have met her somewhere before.
Sera was confirmed to be Shuichi Akai's sister in a previous file. Amuro is definitely Bourbon. That leaves Okiya, he may be Shuichi Akai in disguise.
The question is where did Shinichi and Ran meet Sera? Much less when? Sera has been protective of Conan, and she definitely recognized the name Shinichi Kudo. If anyone has any deductions about the Sera, Ran and Shinichi past encounter. Please share them!
I really hope we doesn't have to wait several more cases for that question to be answered!