>>280288220
The show never focused on their childhood friend bond outside the Oshikko joke and using their backstory to draw parallels to Mako's current friends.
The big MakoKure episode (7) starts with a flashback of Mako's old group that is later referenced to deepen her connection with Kurea.
Even the episode where they visit their hometown is more about the other two childhood friends, how Oshinko hasn't changed after all this time, and again drawing parallels to Mako's current group.
They're childhood friends, but there is nothing special in the narrative about it.