Gojo is in fact, the strongest being in the world. His existence alone shifted the balance of the earth; He's basically invincible.

His infinity allows anything that approaches him to slow down and never reach him which makes him untouchable—that includes rain.

So it confused you, watching Satoru run to you—his hair slightly wet from the rain. He gave you a cheeky smile as he sheltered himself in your umbrella.

"I forgot my umbrella."

Liar. He just wanted a reason to spend time with you.