Mythril Rivets

Taken all the way down to base materials, one Mythril Rivets is 2 crafting steps deep and needs 1 intermediate — Mythril Ingot ×1 — which resolves to 1 distinct raw material totalling 3 units, plus 8 crystals.

That bill outweighs 3,373 of the 13,602 recipes tracked here and 407 of the 1,441 Armorer ones, and 4,464 recipes nest deeper.

Only 4 of those crystals go into the final step; the other 4 are burned by the intermediates, so the real crystal cost is 4 Fire Shard and 4 Ice Shard.

The chain crosses two disciplines — Armorer to Lv 37 and Blacksmith to Lv 38 — so no single class can finish it unaided.

One intermediate outranks the result: Mythril Ingot is a Lv 38 Blacksmith recipe feeding a Lv 37 craft, so that step, not the last one, is the real gate.

Its single raw material is gathered, and no spot for it is timed, so nothing in the tree waits on the Eorzean clock.