This would qualify for Charisma Break if it wasn't for, well, there being barely little charisma in the first place to do the breaking.

Edit: And Chirakashi slips into dialect when she gets flustered. She also slips into a more colloquial style of speech in the earlier arc after getting flummoxed by Syrup, but back then it wasn't exactly identifiable as Kanagawa yet. (it could have been a number of Kantou dialects, including colloquial standard Japanese.)

Hunter/ranger type characters in Japanese fiction will sometimes get this accent*, due to the mountains located in Kanagawa being prime places for hunting game.

(*Other choices include some variety of Hokkaido dialect [or Ainu] for similar reasons, but Hokkaido is far less comprehensible.)