Ok so please help? I know his friend/ brother Gren died. But who is Henry? How is he imp...

Henry is the oldest one in their adoptee family in the past. The one blonde mullet haired guy who told Shin to join his gang. You saw how Shin was there when he was shot dead and nobody knows about it. As for his importance, we still need to see in the future if he really has a big relevance to the story or not.

Thanks! I appreciate the clarification:)