you are a demonic scythe, and for you to become a death scythe, you must slash demons (witch, scourge...) and eat their souls (which are generally human souls and eat obligatory 100 human souls) to be able to win the death scythe range.

so you are Maka's scythe who can become human.(like all demonic objects)

"And there you have it, the 90th soul swallows, there are only 10 left to eat." she says after you ate the 90th soul.