I love this boy

I believe Shuji is the son of Lalah and Char. First, we have Shiiko's death and Shuji's wish. Most likely, Shuji told her his wish was to save his mother, and upon hearing that, it's more than obvious that an image of her own son would come to Shiiko's mind. Additionally, there's Machu's comment that Char smells similar to Shuji, so it seems the reason Shuji protects Lalah is because she is his mother.