FATAL FRAME: Mask of the Lunar Eclipse

During your first playthrough of chapter 1 or 2, if you probably don't have much blue spirit stones to getting an upgrade for both Misaki or Ruka even at the lowest upgrade cost (which is 5 blue spirit stones) for camera categories, then consider creating 2 seperate save slots, one for Misaki and one for Ruka and then get your first upgrades to pop the achievement for both characters in their save slots. Same for the lens upgrades with red spirit stones for both characters if you wanna conserve stones