"I would suggest a blood contract," Ingrounded!Hikaru noted, "But that will not work with... you... Will it? Hmm... But it will work on my counterpart."
She produced a blood contract and handed it to her counterpart. "Sign," she demanded, and Subgrounded!Hikaru glared back at her counterpart. "Why should I?" she replied.
"Do you want to get your soul back or not?" Ingrounded!Hikaru replied.
Subgrounded!Hikaru growled, reading over the contract before biting her finger and signing it in blood. Handing it back to her counterpart, she noted, "When this is over, I am coming for you, 'Uncle'. And you too, 'Father'."
"There. If you get my counterpart's soul, we will help you. Since we can not get your signature, it is binding for us on condition of your response. Meaning, you are not being forced to help us, but if you do not, we do not have to help you."
