OK let's not be too hasty about killing this guy. First, beat him within an inch of his life and make him cough up the location of Rose's bro and sis. Then kill him.
@Purplelibraryguy they have super powers and stuff im sure theres some way to force his dead spirit to cough up the info... or at least torture it out of him!
@Vasqueztion In related plot hole news, he's withholding the info of where he's keeping her bro and sis and so forcing her to use on his behalf her power to enslave any man. Uhhhhh, isn't he "any man"? Couldn't she have just used "lustful oni" on him, and his dad, and got them to give back her siblings and anything else she might happen to want from them?
@Purplelibraryguy maybe if she had learned to use it before they conditioned her as a child to obey without question. She's like one of those brainwashed kids that are turned into killers, some free will but so much stockholm syndrome that it becomes impossible for her to contemplate such a plan.