Oh, see, I was wondering the same thing with leveling up at the Dojo of the Wave.
Since it explicitly tells you that, for example, the Blood Bank Premium Account can’t be purchased without the Basic Account being purchased first, and as another example the Advanced Contract at the Shadow Mercenary can’t be purchased until you buy the Basic Contract, I assumed it meant that that if it doesn’t explicitly tell you, that it is fair to skip ahead.
That is, you should be able to save up to get a higher indulgence and I should be able to jump from Level 2 to Level 4 because nothing says you must purchase them in order.
But let’s see what Sophie says.