In the original manga, it was never explained how Ajisai died.
Ninjas dying while carrying out missions was perfectly normal.
However, the Naruto TV Anime added a lot of scenes involving Ajisai.
One of them showed Konan sending Ajisai on a highly difficult mission, seemingly deliberately sending her to her death so that she could obtain Ajisai's corpse and turn it into Animal Path Pain.
Ajisai was not very old when she died, being roughly the same age as Temari.
But the fact that she was chosen to become Animal Path Pain was enough to prove that she possessed considerable talent.
The Singularity of the Copied Earth.
In other words, the "flaw" in Kamui's Imitation Ability.
—There would always be one place that differed from the original body.
It might be that one strand of hair grew differently from the original body on the previous Earth.
It might also be the shape of the eyes.
Or perhaps it was one's preferences—the food one liked, the things one hated...
It could even be the jutsu one knew, or one's chakra amount...
Taken further, it could be one's gender.
An even greater storm, a butterfly effect, could even turn one person into another!
Take Monzaemon, for example.
Monzaemon, who should have died, not only survived on the Copied Earth but also gained an Evolution Chart similar to Hyuga Sho's.
Ajisai was also a Singularity whose "flaw" had been infinitely magnified, making her completely different.
Ajisai was a transmigrator.
A soul from another world had replaced this world's Ajisai.
Ajisai should have died.
And she really had died.
Her soul had returned to the Netherworld.
But her body continued walking among the living, having been occupied by another soul.
The Earth was too vast.
Kamui's Imitation Ability copied the entire Earth, so it