Kitakami being combini manager seems to be not uncommon depiction, though I never really understood the origins of it.

Is it because "Super KTKM" somehow sounds like large combini chain?

Frawnkenstein said:

Kitakami being combini manager seems to be not uncommon depiction, though I never really understood the origins of it.

Is it because "Super KTKM" somehow sounds like large combini chain?

Nope, 'Super' is just a contraction of 'supermarket' and is used as a generic term. Super [whatever] is a reasonably common name as well (along with [whatever] (food) market).

Frawnkenstein said:

Kitakami being combini manager seems to be not uncommon depiction, though I never really understood the origins of it.

Maybe a coincidence, but I see how her personality, lines and 'easygoingness' would make her an amazing convenience store or supermarket owner.