Atelier Karia's synthesis system is not a menu with a recipe list. It is a map you draw on. This is the single biggest structural change Gust has made to the series' crafting, and it is the system the developers talk about most.
Recipes are built from mana pieces (玛那碎片) and lines. On a recipe map, you connect the fragments yourself — and how you connect them changes what the resulting item actually does. Change the link pattern and you get a different effect; change it enough and the item becomes a completely different object rather than a variant of the one you had.
The design consequence is that a recipe is not something you look up, it is something you construct. Two players with the same set of fragments can end up with entirely different results, and the official framing is that the same material comes in multiple fragment shapes and multiple connection patterns — which multiplies out into a near-infinite combination space.
This is the clearest answer yet to a long-running criticism of the Atelier series: that crafting had become a lookup table. Here the crafting screen is a small spatial puzzle, and the answer space is not enumerable in advance.
Layered on top is Item Rebuilding, which lets you take an item and freely change its effect and its characteristics, and reinforce its values. In practical terms it is the Atelier equivalent of a respec — but more granular, because it operates on the properties of the item rather than on a single skill.
That feature and the recipe map interlock neatly. Because Item Rebuilding exists, a player who misjudges a connection pattern is not stuck — they can keep the expensive part (the fragment acquisition) and re-solve the cheap part (the link). The dependency the original series had, where a wrong synthesis burned the ingredients outright, has been substantially loosened.
Synthesised output is not confined to equipment. It flows into every other system in the game, which is what makes the crafting loop feel load-bearing rather than decorative:
Read end to end, the loop is: gather fragments → draw connections on the recipe map → use the item in the world → eat the item → change form → fight differently → unlock bases → automate gathering. Each stage feeds another. That is a much more integrated structure than the series has ever had, and it is the reason the base-building layer exists at all — it exists to make gathering part of the crafting loop rather than a side activity.
Not yet published: the fragment list, the full effect list, the recipe unlock rules, whether there is a crafting currency or attempt limit, the exact reinforcement values available through Item Rebuilding, and the contents of the season pass recipe pack The Secret Book of Noctrem. The season pass recipe liberation pack is itself evidence that the base game does not contain every recipe — which is an unusual thing for an Atelier release to admit.