Well, the only thing that links them is that they got shrunk. Their pasts, and their futures, are entirely different. Shinichi is in love with the girl he likes, before and after he was shrunk, and is clinging to the past as hard as he can to make sure it won't disappear. Ai would do anything to forget her past, let go of everything, even her sister, and just live a new life as Haibara Ai. She likes being Haibara. Shinichi hates being Conan. See, complete opposites. (I could explain better, but I'm too lazy to do it right now.) One of the 100 reasons why I don't like AiCon or ShinShiho.