How do you make the ultimate keyblade

It differs between each game.

I can explain how to get in Kingdom Hearts 2.

To create Ultima Weapon, you'll need:
- The ultima recipe, found in the basement of Twilight Town's old mansion.
- A handful of the rarer drop items from enemies.
- 1 "Serenity Crystal"
- You need to collect 7 "Orichalcum+" They are located:

- Reward for Finishing the Hundred Acre Wood'
- Reward for Finishing Atlantica
- Reward for Collection 1 of every synthesis material
- Prize for Clearing the Goddess of Fate Cup
- Chest in Centracl Computer Mesa (Tron)
- Chest in Sunset Terrace (Twilight Town)
- Chest in The Brink of Despair (The World that Never Was)

With the ingredients assembled, go to the Synthesis menu in the moogle shop. Select the ultima recepie and use the Serenity crystal of halve the number of ingreditnes needed, so you can perform the synthesis with 7 orichalcum+ instead of 13. This keyblade's stats are 6 ATK / 4 MAG and includes the "MP Hastega" ability, causing your magic to charge faster.