Lelouch is a very determined and somewhat brooding character. He is driven by his desire for revenge and to change the world. Kaguya, on the other hand, is more sly and calculating in a different way. Their personalities could clash because Lelouch may see Kaguya's methods as too self - centered at times. However, they could also complement each other. Lelouch's grand plans for revolution could be enhanced by Kaguya's ability to manipulate the social and political situations on a smaller scale. For example, while Lelouch is focused on overthrowing the Britannian Empire, Kaguya could be helping him by winning over key individuals within the empire through her charm and wit.
Code Geass did start as a manga. However, its anime version became even more widely known and beloved. The manga provided the foundation for the rich story and characters that were further developed in the anime.
Code Geass started as an anime. The manga was based on the anime's success and came after to expand the story for fans. Some elements might differ between the two, but the anime was the original form.