Not just anyone can enter the Limestone cave where the Shikon no Tama came to be. Midoriko keeps intruders out the cave. Her sadness and regret keep people from entering the cave. Inuyasha was allowed in because he sympathized with humans. Midoriko is the miko from whom the Shikon no Tama was born. Midoriko was a miko with great power.
It was during the time that the Court Nobles controlled power. Wars and famine dragged on and on and countless people perished. By devouring the dead and near dead youkai grew in number. Many priests and warriors set out to slay them but one miko known as Midoriko was able to purify youkai souls and render them harmless. She ranked the strongest of them all. After battling for seven days and seven nights a youkai got its fangs into Midoriko. With the last ounce of her energy Midoriko seized the youkai soul, took it into her own soul and forced it out of her body. What she forced out was the Shikon no Tama. She wasn't able to purify the youkai soul. All she could manage was to seize the youkai soul. Although the flesh is gone, inside the Shikon no Tama a battle still wages between the souls of Midoriko and the youkai. That is why the fight isn't over yet.
Shikon No Tama translated is the Jewel of the Four Souls. In this world humans, animals, trees and stones alike are created through four souls.
Aramitama governs courage.
Nigimitama governs friendship.
Kushimitama governs Wisdom.
Sakimitama governs Love.
In episode 94 the Inu-Gumi came across a hanyou named Izumi (Gyouh) that was trying to make a Shikon no Tama. He wanted to use it to become completely human. During the day he was human and his name was Izumi and at night youkai and went by the name Gyouh. His plans was to use the Inu-Gumi souls.
InuYasha's soul would be used for Aramitama.
Miroku's soul would be used for Kushimitama.
Sango's soul would be used for Sakimitama.
Shippou's soul would be used for Nigimitama.
With Kagome's soul and Shards he would have been able to make a core for the new Shikon no Tama.
