The power system doesn't guide the plot. It's just a sign of showing how strong you're becoming. If you're trying to figure out whether your continuing the plot or not, I recommend checking how many girls you've enthralled. Because the story continues as you enthrall more of the girls at the school and everyone outside (besides Hana) are all a bonus. Which at this time ten or so girls should exist that progress the plot.
Those would be:
Maki-A girl you find while exploring a small town area in the morning
Maya-A Nun you can speak with during the early day
Fonia-The pole dancer in the apartments top floors
Laika-A girl you encounter in the park in the evening when you first meet her and then every time after that, you can find her in the bottom apartment in the evening
Saki-The news reporter on the beach
Laila-The girl working out in the park
Hoshino-A cashier at the store CrazyVids