If You Bask in the Sun, You Will Be Invincible. Is There Any Natural Reason?

Awakening ceremony, F-class trash, the laughing stock of the whole city. In the fire station, no one cares about fishing and sunbathing. A-level alien beasts attack, and S-level geniuses retreat. He sighed - "It's so noisy that I'm basking in the sun." One punch. Turn into ashes. Global shock: F grade? You call this an F grade? ! --- One day in the sun for him is equivalent to ten years of hard training for others. His upper limit is the Suns. But he just wants to fish.