This achievement is obtaned by getting a best weapon by Moonlightstones.
Weapon must be at level +6 to start upgrading by Moonlight stones.
Weapons must be strengthened by Moonlight stones up to a maximum of level 5.
Below are weapons that require the lowest ammount of ore to get final upgrade:
(Shard/Chunk/Pure) Moonlightstones required
Short Spear: Sold by Blacksmith Oldwin (20/7/1)
Best places to find Ores:
Moonlightstone shard: Sold by Once Royal Mistress (3000 souls each) in 5-1 Archstone
Chunk of Moonlightstone: Kill the Baby's Nail Black Phantom in front of Fool's Idol (3)
Pure Moonlightstone: Dropped by crystal lizards in 3-3 Archstone