Conan and Xiaolan were childhood sweethearts, but Conan took the dark organization's medicine and was shrunk. But Xiaolan didn't know that Conan was the shrunken Shinichi. Xiaolan regarded Conan as her little brother. Conan and Xiaolan live together. Shirley, like Conan, was shrunk after taking drugs from the Black Nan Organization. Shirley knew the truth behind Conan's shrinkage. Shirley was originally a member of the dark organization, but was later shrunk after taking the shrinking drug. Now, he is living in Dr. Ali's home. Like Conan, he is a fallen person in the world. His body has been shrunk, but his mind is still mature. Shirley has an indescribable feeling for Conan (approximately likes her) but Conan still likes Xiaolan wholeheartedly...

Reference: Brain hopes you can hire me, I have worked so hard to type so much