When K drives Shuichi back from the airport, you can see a doll hanging from his rear view mirror. The doll closely resembles the character Judy Winchester, K's wife who's introduced later on in the manga.

Ken, a band mate in ASK, is never once seen without sunglasses.

When Shuichi is bustling around Yuki's apartment with his belongings, he holds up a magazine to ask if Yuki has read it. If you look closely, you will see the magazine has Yuki and Shuichi on the cover.