She planned everything

Rikako planned it. She took her friend Yumi to the airport, knowing that Yumi could not go when she changed the destination from Osaka to Tokyo at the last moment.

We already know that Rikako had planned all along to go to Tokyo, and Yumi also says this in her telephone call to Taku. Rikako already had the tickets to Tokyo. But I think her plan went further.

She disappeared in the bathroom on the airport, knowing that Yumi would call Taku. She also knew or at least hoped that Taku would take her place on the flight if Yumi stood back.

Perhaps the only thing she did not plan was that Taku would sleep in the bathtub. (:-)