After Dante revealed to the crew that he had infused Astaroth's soul with Forty-two's body, they went completely silent from the shock.
"H-hey… What do you mean it's Astaroth's soul?" Zac inquired with a hint of fear in his voice.
"It's not his soul—only the frame of it," Dante clarified, but his team had no clue what he meant, so he had to elaborate further.
When Dante killed Astaroth, he turned his soul into a soulstone, which the warlock had done with many other demons in the past.
Demon's souls could be used for different warlock activities. However, most of the time, the warlock would simply absorb the power of the demon, increasing their own reserve.
He used the soulstones that he gave to Zac and Megan as an example, explaining that those soulstones that allowed them to control umbra were the frame of many demons' souls mashed together.