So T-card. it has been featured in some of this 4-koma long run.
The first one I can found is on post #3537617 where Sanae introduces the gag revolving around conbini.
The second one is found at post #4644315 where Marisa asked by mysterious voice whether she wants power with a price and it accepts T-points.
This one have credit card that support T-point, which is some part of the world transitioning to semi-cashless society... The fact the goddess of the spring in honest axe fable in here is also telling, Aya have lost her pen there, Flan also rejected the goddess offer when Remi falls in there.