In 'brunhild the dragon slayer light novel', the main themes are courage and power. Brunhild has to have a great deal of courage to face dragons. Dragons are often depicted as extremely powerful and dangerous in fantasy, so her courage is put to the test. And as she slays dragons, she gains power, whether it's physical strength, magical abilities, or just a reputation. There could also be a theme of destiny, like she was born or chosen to be a dragon slayer and is following that path throughout the novel.
Well, one of the main themes is adventure. Brunhild embarks on a journey to slay dragons, which is full of unknowns, challenges, and new places to discover. There's also likely a theme of heroism. Brunhild is taking on the role of a dragon slayer, which is a heroic act. She is probably saving people or places from the threat of dragons, so heroism and self - sacrifice could be part of it too. And, as mentioned before, the development of her character as she faces these challenges is also a key theme.