WHAT

Does 'Nanako' sound like pineapple in Japanese or something?

Part of the artist's commentary

ちなみに、3人が話してるのは「酢豚にパイナップルを入れるか、入れないか」です

Incidentally, the three is talking about "Should pineapple go with Sweet and Sour pork".

... so... where does Nanako come into this again? I'll just say Souji is telling them Nanako likes pineapple with pork or something.

in my mind, maybe soujiro asked the 2 of them what would be the best to present nanako from that restauran while hamuko suggesting pinnaple and minato not prefer that

OR

while treating hamuko and minato to ramen(?) shop, soujiro asked what flavor they like to add, and thus soujiro says that sour pork with pinnaple is recommended bcoz nanako like that flavor very much.

Pineapple reference http://www.youtube.com/watch?v=keDA_6vxsVk