If your guess is right, then, I think this suggestive hint on Akemi's message will fit into the Akai=Okiya theory well. Okiya proposed to live in the Agasa residence, where Shiho lives too. I guess Akai tried to fulfill Akemi's wish and wanted to make sure Shiho is safe by living together.Chekhov MacGuffin wrote: My top theory is that it has something to do with Shiho. I think Akemi knew she was probably going to be killed, but still went through with the billion yen heist on the faint chance the org was being honest. My guess is that she was asking Shuu to find a way to spring her sister from the org or at least protect her somehow. It seems like something Akemi would do...
Of course, this idea requres that Akai has already noticed that Ai=Shiho. But I believe Akai has at least suspected this possibility and tried to be sure enough to convince himselfe.