How do I improve the ebony blade [duplicate]

Solution 1:

The Ebony Blade is Mephala's Daedric artifact. It is not connected to Boethia (whose artifact is the Ebony Mail).

The Ebony Blade cannot be improved by smithing. This is possibly explained in Admonition Against Ebony which states that: "Not even the hottest fires of the Skyforge could melt it; indeed the coals themselves seemed to cool when it was placed within," revealing the sword's immunity to heat or normal forging/smithing techniques.

The sword's enchantment can be improved, however, by killing friendly characters. This includes followers and anyone for whom the dovahkiin has completed a quest or favour.

Source: http://elderscrolls.wikia.com/wiki/Ebony_Blade_(Skyrim)