Yeah you didn't know that that's what this sword's name actually means? Kagotsurube Isshin - One Will of a Cage Fishing for a Bottle. What does that even mean? Hell if I know!
But the lore! The lore is so delicious! And here I was thinking Kazuha's quest had nothing to do with Scara.
What you don't see the Kagotsurube? It's right here.
籠 Cage 釣 Fishing for 瓶 Bottle!
This is actually part of the name of a kabuki play. Remember how Kunikuzushi and Kuronushi are also from kabuki?
The full name is Kagotsurube Sato no Eizame and it's about well a ton of stuff first and then all the way at the very end the main character finds the cursed sword Kagotsurube and kills his lover with it. But I'm getting ahead of myself.
In the play the story goes that an ugly looking dude sees a very beautiful courtezan Yatsuhashi. He instantly falls for her. He is very gentle and honest (seen as a defect by Ei ) and gains the trust of those around him. He is so enamored with Yatsuhashi that he introduces her to all his contacts and even brags about buying her out from the brothel to marry. What he doesn't know is that Yatsuhashi actually has a husband Einojo and one day he finds out about how infatuated Scara-I mean Jirozaemon is with her. Jealous he forces her to break it off with him and she reluctantly does. Heartbroken he flees.
Months later he comes back and he seems very happy. The brothel's other workers welcome him back and Yatsuhashi apologizes to him. He asks to sit with her in private and offers her a drink. Then suddenly his attitude twists and he says "this is to be your last drink" and whips out the Kagotsurube killing her in a single stab. (ok maybe Ei has a point 
)
And they lived happily ever after! (him and his cursed sword 
)
I previously theorized that this is something like Scara's story. He was once a naive and gentle person. Eventually one day he meets a girl from the Niwa clan. Infatuated with her he eventually helps her to save the Gokaden by having them flee to Snezhnaya after failing to forge Ei's Goshintou. But again in my theory I said she might already be married so once he's helped her she apologizes and admits the truth that she has a family. Later on Scara meets that family in the form of Kaedehara Yoshinori. He had gotten bored of "destroying" the Gokaden but he found a new identity. And then he stabbed her through with his cursed sword! No he's a little more ambitious than that. He plans to stab the whole country through with his cursed sw-Gnosis! 
Could there be any truth to this? Maybe maybe not. But I can't really figure out any other reason why MiHoYo would bring up a reference to that kabuki play. It's not like Kazuha or his ancestors are known to frequent Inazuman brothels or anything and helping an ugly dude kill his courtezan gf doesn't sound like Kagotsurube Isshin's M.O. either lol
Tips and Tricks from a Super Casual Genshin f2p
