Don't worry, there are two types of girls in the game. Special ones and recruitable ones. The special ones are the main girls in the story (Lava, Sena, Noa and Nera) that will get bigger as we spend time with them. As for the recruitable ones, we can make them join our team with money and they will get bigger as they level up. These recruitable girls will have up to 3 levels of growth (Like in Pokemon) although some girls will not grow. (The elemental ladies.)