For this achievement you must have Seraphina create the Holy Grail item. Seraphina must be at IC Level 6 and you must complete the General Shop Upgrade Quest(for the Novo Herb) and the Alchemy Upgrade Quest (for the recipe). This can also only be obtained end-game on normal or higher difficulties, unless you kept the materials found earlier in the game.
For the General Shop Upgrade quest, in Halgita talk to the Old Nightwhisper found in the church. Then talk to the General Store Owner and she will ask you for 3 Lentesco Wood. Lentesco Wood is a rare drop from Lumpers in the Bihar Mines or Mandragoras in the Cobasna Timberlands. After obtaining 3 talk to the shopkeeper and you will be able to buy new items.
For the Alchemy Upgrade Quest, in Fayel Castle enter the small left room in the hallway and talk to the Alchemeister (only available after loading your finished game save), he will ask you to bring him 1 Dragon Eye. Dragon Eye is dropped by Lava Gluttons in the Cobasna Timberlands section of the Seraphic Gate. After obtaining one talk to the Alchemeister and he will give you more alchemy recipes including the Holy Grail.
Now for the Holy Grail you will need the following materials:
10 Miraculous Medicine- Bought from most item shops or from Genma.
1 Atlantis Metal- Rare drop from Hill Gigas in the Graad Woods section of the Seraphic Gate, or can easily be bought from a shop with the "A" Voucher.
3 Claridian Medicine- Can be made by Kiriya and require the following materials:
1 Mysterious Medicine- Easily made by Kiriya
4 Novo Herb- Can be bought at the Halgita General Store after completing the upgrade quest.
1 Green Berry Potion- Can be made by Kiriya or dropped by many enemies.
Note: Make sure you save before you attempt to create the Holy Grail as it fails very easily.