Board Thread:Theories and Speculation/@comment-3523655-20180918083440/@comment-1458758-20180918183703

Alright, did some digging. I think this one relates to the Japanese myth specifically.

Totsuka sword doesn't refer to a specific blade, but a type of sword of which several appear in myth. The notable one however, comes up in the legend of Yamata no Orochi.

Susanoo uses a Totsuka sword called Ama-no-Habakiri to lop off Orochi's heads and tails, in which he finds the Kusanagi sword. This is also probably why the Totsuka is summoned from a gourd since Susanoo got Orochi drunk in order to kill him.

So in relation to Naruto, we're literally dealing with one sword (Kusanagi) that is derived from the feats of the other. The obvious parallel being when Itachi sealed Orochimaru's Orochi form into the Totsuka.