She's the mother of Kaito Kuroba. In the TV special she was away in Las Vegas at the time and in a video message to her son said that she knew he'd probably "be very busy very soon", implying that she knew about Toichi's secret room, his identity, and that Kaito would likely become Kid.

Spoiler

In Detective Conan chapter 733, it was revealed that Chikage was once a phantom thief herself known as Phantom Lady. A background story of this is revealed in two new Magic Kaito chapters, which included Toichi's first heist. In it, Chikage met Kid who then saved her life and fell in love with her. She mentions about this later, which sets the stage for the chapter. According to Sonoko Suzuki during the Ryoma heist, she was the great thief known as the Showa Era's woman of twenty faces. She wore horror make up and was very popular for only targeting large companies and very rich individuals with unscrupulous earnings.