User blog comment:FairyRaven/Fairy Tail Chapter 456: Orders, Review and Commentary/@comment-24553184-20151010124141/@comment-4933386-20151010142232

To be honest, I think making a character naked is not just fan service, it sort of shows the vulnerability of the characters and shows them their worst. Such as when Yukino was forced to stripped down, being humiliated by the master whom I forgot his name. When several characters was stripped with nothing while in captivity against Tartarus.

But in this case, Brandish is still dominant and can blackmail Lucy to get in the bath with her. But I believe Brandish wanted speak to Lucy equally (revealing everything kind of) without an actual battle which I think something Brandish doesn't like.