I don't think the noble's last name is Asagi. That's just Shigure's name. And maybe they changed the family crest to light blue as a small tribute to her.
Also, just to clarify, it's the hammer's true form that's a pillar. Shigure is Shigure.
A very late correction, but that line is actually about "surviving nobles".
In the Heian Era, there was a prostitute who was taken as a mistress by a nobleman. Due to the difference between them, they would never be allowed to marry, but the prostitute loved the nobleman, and the nobleman also loved the prostitute.When a power struggle occurred around the nobleman who was involved with the prostitute, he got wrapped up into it, and in the end, someone set fire to his estate, and they were murdered.The true form of this cursed item isn't a "hammer", but a pillar of the burned estate that transformed into a "handle" due to malice.Now, they say that the family crest of murdered nobleman is "Asagi" (light blue).Afterwards, from the ruins of the burned down estate, a pillar and the body of the prostitute vanished."Grudge Hammer" (Golden Hammer +1 Cursed Item)Prop Explanation #2Several days later, the burned corpse of a woman appeared before the nobles who started the power struggle, and one by one, they were bludgeoned to death. This incident was resolved by a nine-tailed white fox and a master martial artist calling herself "Tatsunoshin", and the surviving nobles entered a monastery.