That is not a rough estimate. It is the exact per-level cost array pulled straight from the current build for skill after skill, hero after hero. Level 1 asks for 20 books. Level 9, the last step before max, asks for 400. Add the nine numbers and one skill to full costs 1,245 books total.

📚 The Nine Numbers

The curve runs 20 → 30 → 45 → 60 → 90 → 130 → 200 → 270 → 400 across levels 1 through 9, out of a max level of 10. We checked this array against a wide sample of skill entries in the current build, including active skills, passive skills, and formation skills, and every one of them matched. The book itself is one shared resource, not a hero specific item.

The shape of the curve matters more than the total. The first three levels together cost 95 books. The last three levels alone cost 870. That is 70 percent of the whole climb sitting in the final stretch.

🦁 Eight Slots Same Curve

Beast Queen: Diana carries eight skill slots, and every single one of them runs the same 1,245 book curve. Maxing all eight costs 9,960 books, not counting any hero specific unlock requirements tied to those slots.

Eight slots is not unique to Diana. Every military hero we checked in the current hero dataset carries the same eight slot layout. If your hero pool is even three or four heroes deep, book demand adds up fast once you start maxing more than one skill at a time.

🔍 Check Before You Save

This curve is a strong default, not a guaranteed rule for every skill in the game. We sampled a wide set of entries and every one matched, but we did not check every skill ID that exists. Before you commit a stockpile to one specific skill, open that skill's own upgrade panel and read the level 9 cost off the screen.

📋 Spend In This Order

Levels 1 through 6 only cost 355 books combined, so push several skills that far before you specialize. Hold your book stockpile back once a skill hits level 7, because levels 7 through 9 alone eat 870 books on their own.

Positive spend: you split 400 books across two skills to get both to level 5, keeping your formation flexible while you decide which skill actually matters for your march. Flip side: you dump 400 books into one skill's level 9 push, then a better formation option opens up and the other seven slots are still sitting at level 3.

Which skill on your main march is still stuck below level 7?