It's summertime, and eleven-year-old Marcus goes with his mother to a new city, where she'll be working for the summer. Marcus is looking forward to it because he knows he can be himself there - the person he really is. Within the first day of arriving, Marcus meets Mikkel, a neighbourhood boy who looks totally dangerous with his aggressive and energetic appearance, and with his body full of tattoos. It turns out the tattoos are made by Mikkel's brother and are actually in Indian ink, but still. Mikkel challenges Marcus in a number of skateboard tricks (both are addictive skateboarders), and after a crash where Mikkel helps Marcus, they become best friends. Blood brothers - bros! - something that means you'll do anything for each other and always tell the truth. But Marcus is struggling with a specific issue. Should he tell Mikkel this special thing, something that effects Marcus' whole life? Marcus was assigned female at birth, although Marcus has always known he is a boy. It is just the others around him who have a hard time understanding, including his friends at school, his grandma, and his father. King Bro! is an emotional, poignant look at knowing who you are, but struggle with knowing how you'll be accepted for being your true self.