Mahou Shoujo wa Shuuchishin de Tsuyokunaru

Mayu is a girl who was chosen by her idol, the magical girl Hisame-senpai, to be her successor. The stronger a girl's sense of shame, the stronger she becomes. But after a battle with Noktan, a resident of the demon world, Hisame-senpai lost all sense of shame and became comfortable appearing in public dressed almost naked. Having been chosen as her successor, Mayu transforms her shame, which had her on the verge of death from embarrassment, into power and challenges the battle. (Source: Natalie, translated)