>>2281908Knowing the author, we will more than likely never see any background about their relationship, however mysterious it is, he cares about quick action and ecchi.
Galil seems to bee the only person that Sako respect, how she earned that respect, we will probably never know.
One very interesting theory is the fact that the IMI Galil is modeled after Sako rifle schematics in the real world, this connection would technically make them more like sisters, but the author hasn't confirmed or denied this, it could have nothing to do with them as a pair and could be complete coincidence, the only thing he mentioned that would bring them together is the fact they are both Knock-off Kalashnikov, or as Ichiroku once cleverly put it, "Kalashknockoffs".
I do hope one day Tennouji will get his head out of his ass and give the girls more depth.