If we're talking about coincidences that bring two halves of a story together, the ending of this chapter reminds me of George the (fake) "Marine Biologist" epic tale of retrieving a golf ball from the blowhole of the beached whale (where the golf ball turned out to be Kramer's) on one of the greatest episodes of Seinfeld ever.
Keeping it within Minami-ke, another great coincidence was Kana inadvertently kicking Chiaki's best friend "Yamada" (a rock) back in to the truck he originally fell out from in the first season of the anime.