The monk who stole the Kusanagi no Mitsurugi ran away using the former North Gate called Seisetsu-mon. After that, the northern direction was considered unlucky and the gate was blocked off.
They say that the sword was relocated to the Imperial Palace after the theft for its protection. However, 18 years later its overwhelming spiritual power was blamed for causing the Emperor to fall ill, so they returned it to Atsuta Jingu.
Five hundred years later, the sword appears in the Battle of Dannoura. The following is the final scene of The Tale of the Heike.
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The Heike clan ran away from their enemies, the Genji clan, bringing along the three sacred treasures and the child Emperor Antoku with them.
After a naval battle that ended in their defeat, the Heike family jumped into the sea one by one to end their lives. As the young emperor’s grandmother led him to the ship’s side, he asked her “Where are you taking me?” She responded, “To a capitol at the bottom of the sea.” And with that, they jumped into the sea while holding the Kusanagi no Mitsurugi.
After the battle ended, the Genji clan desperately scavenged the ocean floor but couldn’t find either Emperor Antoku or the sword.
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Some people might be wondering -- if the sword was lost at sea, then what’s enshrined at Atsuta Jingu?
It’s said that a copy of the sword was located at the Imperial Palace, which must have been the one the emperor took to the bottom of the sea. It’s possible the original never left Atsuta Jingu.
The Tale of the Heike is a collection of oral stories, so it has questionable reliability as a historical document. Instead of lingering on that, let’s focus on the road in front of you and the people who use it. This road was the official approach to the shrine until the Edo Period, when travelers who believed the tales of the Kusanagi no Mitsurugi would come and pay homage. The facts themselves are less important than the way they make people feel. How does it make you feel?