How do you unlock the girls in robozou?

In RoboZou, you unlock the girls by progressing through the game and completing specific challenges or missions. Each girl typically requires you to achieve certain milestones, such as reaching a particular level or collecting a set number of items. Additionally, some characters may be unlocked through in-game events or by achieving high scores in various modes. Keep an eye out for any special requirements or hints provided in the game!