Remember that earlier, Mieru said that spiritually weak youkai are invisible (and also a puchi), and here, she's saying that she directly damages the spirits of youkai she attacks like this. The implication, then, is that any youkai significantly spiritually damaged would become the invisible puchi type... just like Shiki.
I think the Reiga Style was used on Shiki- I think on the right is her original form, and on the left is her current.
If that's the case, then Reiga did indeed commit a crime. The Zashiki Warashi on the, right was waifu material for sure.
on a youkai... ever ag... ain...So 'course...I won't use it...'Tis lovely and warm♪Captivating Fluff ReturnsAnd if their soul gets damaged, it can never be healed again.they get hurt right to their soul, see...About that... If I use it on a youkai...That house-breaker dealie!That's right!You mean spiritual power, yeah?Why didn't you go all "baaam!" and stuff!?This sofa is so warm and soft... it's the best...Zzzzz....Mie...?Ahh...Mie!