This mod is called Demonic's Blessing. And as you can probably imagine, it's a bit OP, or Over Powered. It's a model of a daedric greatsword. It deals a lot of damage and an absorb health. It can be found in Bleak Falls Barrow right in front of the word wall for Unrelenting Force. So you can get it before you fight the Draugr overlord. If you don't want to use or something. You can still pick it up, and it will not hurt you at all as it weighs nothing.

If you don't want to go through BFB, or you've already gone through it, you can make it once you have Arcane and Daedric Smithing perks, but you'll find it's not the simplest recipe. I've one this on purpose from preventing people on making multiple copies. I've also made tempering a bit challenging for the same reason. I will not be updating this as I'm satisfied with it, but if you want to make some requests you can. I mainly do weapons, armor, and follower mods as those are the easiest to do for me. If you have any questions, feel free to ask. I'll try to answer them as best as I can.

Compatability:

Immersive Armors and Weapons: It works fine with them.
PerMa: Also works fine with it. Heavy Weapon Skill increases as you use the weapon.