Rank for Shop

[사나 <3]

How do you increase the shop rank, do I just spam buy? I'm currently doing the Zessho Stage. But my Shop Rank is still around 7 only. This should be the same max rank as previous games right? Max is 12?

[Zukabazuka]

The more HL you spend in the shop the higher it goes and yes customer rank is max 12

[Astasia]

Shop rank increase by passing the new bill for it gained after completing most main story chapters. Customer rank increase by spending money on the store.

[사나 <3]

I'm good now for this, I just spammed buy the max level items about 900 in total it shoot me straight from rank 7 to rank 12