"Promise"

I got reborn in my favorite manhwa after i died in a fire accident.
When I opened my eyes, I found myself in a dark cave, but after I walked for a while, I found a boy with dark brown hair and tattered white clothes lying on the ground. Then he woke up and I looked into his eyes. I was surprised that he had two golden eyes. He is the hero of the story of the Tower of God!!! bam the twenty fifth And I am... his sister? What is this mess?!