@wrzlbrnft@troet.cafe My guess is that adding the adjective ending -i makes the name sound cuter and less boring than just using the name of the prefecture, which means "blue/green forest" (green was historically considered a shade of blue in the CJK sphere - green traffic lights are still called blue in Japan to this day, for example) - with the -i it spells out Blue Forest in a more literal sense, hence the blue livery, logo with cutesy blue trees growing out of the train and such