SHY

In the middle of the 21st century, the world was on the brink of World War III. But superheroes from across the globe appeared and helped bring an era of peace. With the crisis averted, the Heroes returned to their home countries where they now help with domestic matters.

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From Yen Press:
Earth was on the brink of a third World War when super-powered individuals came forth from each country around the globe, ending the conflict and ushering in a new era of relative peace. Among those heroes, Japan is represented by a timid young girl known as “Shy.” She may spend more time worrying about her own shortcomings than she does battling villains, but she'll show the world that despite it all she still has the heart of a hero.