As evil as Miji and the Genies of unhappiness are, they are still bound by the law of Genies. They must grant there 'masters' wishes upon revival.

There are always those that would use a genies powers to do harm to others, or to wish for something selfish. As such it is the two classes of genies that try to show humanity the error of its ways.

Now while these object lessons tend to lead to so many bad things.

Sometimes, there are those bright and shining people that give the most evil and vile of the gen's of unhappiness a run for there lives. After all. These bright shining examples are the ones that wish for things that are to help people and those they know.

Which would be good for a Gen like Eira who feeds of the good of others wishes and always strives to create harmony and happiness.

However its a far cry for 'good' for Miji, who in this case. Didn't just lose the nurishment for the deeds she could do with this human. She just lost out on all the misery she had when she had to re-write history to undo all the trouble she had caused in her 750 year stay.