It's just a legendary IRL sword that supposedly made people around it want to be conquerors. And that is almost only because Nobunaga got it from his 250,000 to 1000 (in Ikesen, 2,500 IRL where he was married so had some of in-law troops) battle, and then gave it to Hideyoshi who also gave it to Ieyasu
So in Touken Ranbu, the sword has a personification and is all "wahhhhh why does everyone want me so much T_T" (and hates Nobunaga) but it's not actually cursed
The "legend" curse is that it turns you into a conqueror, like Nobunaga said. But even he sees it as superstition. And in IkeSen Yoshimoto Imagawa is still alive, because AU time travel Shenanigans, so he's constantly DRAMATIC AS FUCK like "the sword must be crying right now T_T" yes
The second is that Yato is a reincarnated god that was swiped and used by father which is incredibly detailed and documented which also seems somewhat plausible due to many indications
People like Tsukuyomi because outside of the very obvious moon motif that Yato has going for him as far as powers go, this messing with people's fate can cutting ties of fate is sort of moon-related in mythology
There was more like Tsukuyomi being cast out of Heaven and when Yato wants to join he's asked if he will capitulate to Amaterasu's will and is seated with the other rebels who he doesn't know
lot of power for a little no name god don't think about itHiyori: [does the thing]
Yato: /SIGH/