Eisuke's name comes from Bondo (ボンド), the Japanese pronunciation of (James) Bond
Eisuke and Hidemi are brother and sister since their eyes are identical, so it can assume that Akai and Sera are brother and sister too since Sera has bags under her eyes identical to Akai Shuichi's. Also, Sera Masumi's name is also incredibly similar to Mobile Suit Gundam character Sayla Mass (セイラ・マス, Seira Masu). Akai's name is derived from Sayla Mass's older brother's name, Char Anzable. Furthermore, Conan thinks Sera is familiar somehow, like they have met before or she looks resemble to someone he knows.
If they are brother and sister, then either Akai Shuichi or Sera Masumi is fake name, then Akai or Sera is a real surname among them. Perhaps Shuichi and Masumi are real names but they are adopted by different parents after their real parents passed away when they are little. Or maybe one used father's surname, the other used mother's surname after their parents separated. And Akai once using a fake name Moroboshi Dai while infiltrated BO, so maybe Akai Shuichi is fake name too, but there is no need to use a fake name in front of his fellow FBI members.
The title of File 604 is "Older Sister and Younger Brother", a chapter where Eisuke and Hidemi confirmed as brother and sister, then when Akai and Sera are confirmed as brother and sister, the title of that chapter will be "Older Brother and Younger Sister".
Let's compare their eyes to see if they are identical.
Their posture is very alike right?


Compare Sera and Akai's face when they're annoyed









