One main theme is isolation. The Shield Hero is isolated from the other heroes and much of society at the start. Another is perseverance. Despite all the hardships, he keeps going. And there's also the theme of justice, as he is wrongly treated and we expect him to find some form of justice as the story unfolds.
The main themes include betrayal. He is betrayed by those around him early on, which sets the tone for much of his character's development. Additionally, self - discovery is a theme. As he faces challenges, he discovers more about his own strength and abilities. Redemption could also be considered a theme in a way, as he aims to redeem himself in the eyes of the world that has wronged him.