Aoi’s accent is subbed a little more aggressively in this episode. Somehow this is the first time our hand’s really been forced. Apologies for the inconsistency; it may be similar moving forward.
Shingen’s banner says 風林火山, a phrase for which he is quite well known. You can look it up. The ‘hidden bath’ (隠し湯) is used to describe baths that allegedly were for the private use of lords and such (ironically, they’re in a town this episode called Shimobe, which could be read ‘peasant’), and gives a sense of a higher quality. 隠し kind of means ‘hiding’ or ‘a state of hiddenness’ more generally, and so it makes perfect sense in Japanese when Aoi interprets it as something more like ‘hiding bath’.