I hadn't actually noticed this. I think it's because it's just modern enough that it doesn't feel out-of-period for her to be writing like that, although precisely what "period" is for Ōyodo is hard to figure out. Her construction is presumably much later, but her voice is spot-on for an overly formal character (or a stereotype Japanese naval officer) circa WW2.

If she'd gone full Age of Sail or been like this in person, it would have been off, but this works nicely for a letter, particularly since she's writing to somebody who would be a superior officer if not for the whole Admiralty Code problem.

Peter Eng
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Insert humorous comment here.