Seikai no Monshou, Ginga Sengoku Gunyuuden Rai Recommendations
Being of the same Sci-Fi genre of space opera they share some common elements like the growth of a young boy that becomes relevant in the story as he evolves and both are in an environment of war between space reigns with all the political issues and combat action of spaceships. Sekai no Monshou (aka. Crest of the Stars) takes a more personal aproach to the story and GSY Rai (aka. Thunderjet) takes a more action and great scale approach.
Both great and dramatic stories with enough character development one more serious than the other.