How do I make it stronger? And I heard the sword is bugged if so how is it?

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Are you just referring to any Ebony sword? If you want to improve it on a Grindstone, you'll need an Ebony ingot and some decent skill in Smithing.

He means the daedric artifact known as the "Ebony Blade". It doesn't get stronger, but instead has a very nice enchant. It is bugged in that it used the incorrect weapon skill if I remember right, although I don't really remember which skill it is supposed to use ATM. I THINK it is supposed to be based off of one handed skill, but instead uses two handed.

no the special one lolll you get from some quest

It was a one-handed weapon in Oblivion; now it's a two-handed one. It went from a katana to a dai-katana. As for powering it up, you have to kill someone who trusts you. What that means precisely in game terms I'm not sure. Never bothered with it as I'm a sword and shield kinda guy.

Kill people who trust you. Wives. Companions. Quest-givers.

Increasing the "Armsman" perk in the one-hand skill tree raises the attack damage of the sword. Using enchanted items that boost one-handed skill also increases the damage.

I'm not sure whether killing those who trust you increases the attack damage or the drain health enchantment. I've read different opinions.

I'm not sure, although I've been told it doesn't, if raising your one-skill has any effect on the attack damage. Regardless, choosing the Armsman perks (1-5) definitely increases the attack damage which is problematic because when using the sword your two-hand skill is what increases.

To get the max benefit, besides killing friends, you should have as many Armsman perks chosen as you can before getting the sword.

EDIT:
I believe the Ebony Greatsword looks just like a katana and it's two-handed. In addition, it's NOT bugged. With a high two-hand skill it will cause more damage than The Ebony Blade.