(Everyone keeps taking my ideas. Should I be happy or sad? Reincarnation, the use of the spirit world...I think I am proud.)
"The proposal is simple, and acceptable. I will assume I am free to design it as I see fit..."
As the deal is struck, the hammer of creation begins. I temporary put all my attention into making the blade. A claymore seems like it would fit his description, one the size of an ordinary man. First, I make it out of solid Damascus steel. I cut the edges to a single molecule, and make the blade eternally sharp. On the hilt, the very bottom, I add a single button in the shape of an elongated diamond. Pressing this causes it to sprout flames from its center outward, in a blaze the wielder can control. I attune the hilt so it will only accept the man it has been created for, other hands will be rejected and the blade will grow heavy. I practice a few swings in the void until I am satisfied with its balance. Then, having completed the basics, I continue to the aesthetics. Knowing he has the power of magic, I add several gems in the shape of elongated diamonds along the hilt, fit for storing magic that may be released into the blade. I make the blade unbreakable, and give it the power to return to its owner on demand, no matter what the distance. Lastly, I camelionize the blade, so it may change from any color its user wishes for pure ascetic purposes.
"It is nearly done. The one feature I would like to add would be sentience and sapience, though I would require you to pay a share of the essence required for that.