The color page with the caption stating this is the last fight for the 13 Captains has exactly 13 characters. All of which either have been showned to have powered up or suspected.
Shunsui, Soi Fon, Yumichika, Ikkaku, Iba, Hisahi, Rukia, Zaraki, Byakuya, Hisagi, Renji (10)
Ichigo, Chad, Orihime (3)
My crackpot theory is you're looking at the Gotei 13 at the conclusion of the series. That is why Shunsui said Ichigo will not return from SS and that they can visit him with those tickets. Maybe Toshiro becoming a zombie (implying he's dead) is the catalyst for a bunch of deaths coming up. Perhaps Rangiku or Momo is going to show up soon with a bankai and kill each other off. Nah, too predictable. Who am I kidding, TK will take another puff and just jedi mind trick this shit back to normal.