Can be anything from any source, movies, books, comics, video games, manga, anime etc.
Pic related is mine, the dragonslayer from berserk. I like it because it's simple. It's just a big fucking sword, no fancy bells and whistles like enchantments or spells.
Second runner-up is sting from lord of the rings, I like that it glows blue when orcs are around and it can be used in the dark as a light source.
Balefire itself is more of a spell than a weapon, but also very cool to have a “weapon” that directly attacks the fabric of reality to remove the targets thread of existence.
Yeah, I guess what I like about it is the fact that it isn't a weapon really, but at the same time winds up being the most powerful weapon against The Dark One in the end, the subversion of expectations for magic swords feels good and well executed there.
Yeah, I like how it takes the form of a sword without being able to literally be used as a sword. It can abstractly be viewed as being used as one, but that separation exists