Unsure what the hat is called, as well as the shirt and dress (though I just tagged them as "white kimono" and "red/pleated/high-waist skirt"). I think it's Chinese style, but no clue on specific names
Edit: A friend has suggested "wu shao mao" as the name of the hat
Updated
Azur Lane comic anthologyIchijinsha-sama is releasing it for purchase on February 3rd, 2021