Kosuzu's pun is originally about "Iron Are!?" being similar to "tetsuarei", which means dumbbells. In a pale imitation, I tried to adjust it to be about the Miare Maiden instead, even though the end result no longer has much to do with the context.
Similarly, the original title of the book literally means "Through-Are-Power", which is nonsense but happens to be pronounced "tetsuarei".

"Beefed up" is just a bit of opportunism on my part.