Dwarven Mythril Rapier

Taken all the way down to base materials, one Dwarven Mythril Rapier is 2 crafting steps deep and needs 4 intermediates — Dwarven Mythril Ingot ×2, Dwarven Mythril Nugget ×1, Lignum Vitae Lumber ×1 and 1 other — which resolve to 7 distinct raw materials totalling 24 units, plus 48 crystals.

That bill outweighs 8,926 of the 13,602 recipes tracked here and 1,346 of the 2,216 Goldsmith ones, and 4,464 recipes nest deeper.

Only 14 of those crystals go into the final step; the other 34 are burned by the intermediates, so the real crystal cost is 27 Wind Crystal and 21 Fire Crystal.

The chain crosses three disciplines — Goldsmith to Lv 78, Blacksmith to Lv 78 and Carpenter to Lv 78 — so no single class can finish it unaided.

All 7 raw materials are gathered, and one of them is time-gated: Gold Ore (9:00). That window comes round once per Eorzean day, every 70 real-world minutes.

Of the intermediates, Dwarven Mythril Ingot has the widest use: 168 recipes call for it, spanning seven of the eight crafting classes.