Well, power and its consequences might be a theme. As the characters pursue the way of the sword, they gain power, but that power may come with a price. They might have to face moral dilemmas on how to use that power. Also, honor is likely a theme. In the world of swordsmanship in the bl novel, honor could be tied to how one wields the sword, whether in battle or in interactions with others.
One of the main themes could be self - discovery. The characters in the novel might embark on a journey of the way of the sword, which forces them to look deep within themselves to understand their true potential and purpose. Another theme could be loyalty, perhaps loyalty to a particular swordsmanship style or to a master or comrades within the context of the sword - related world.
Love and friendship are likely to be main themes. In many BL novels, the relationship between the male characters often involves a deep sense of love and also a strong bond of friendship.
As I'm not familiar with this particular novel, it's difficult to say. However, common themes in BL novels can also include social issues such as homophobia and how the characters navigate through a society that may not be fully accepting. Maybe 'The First Commandment BL Novel' also touches on the power dynamics in relationships, as some BL novels do.
One of the main themes is probably the struggle with unrequited love. Often in BL novels, one character may have feelings for another who is initially unaware or hesitant.
Love and passion are the main themes. It shows the intense feelings between the characters.
Another theme could be self - discovery. The characters often grow and learn more about themselves through their relationships. For example, they might discover new aspects of their personalities or their desires in life.
Another theme is justice. The characters strive to uphold justice in a world full of challenges and corruption. They fight against the wrongdoings and try to make the world a better place.
Love against all odds could be another theme. In a BL context, the two male characters falling in love in a situation where they might face external opposition or internal doubts due to their initial enmity. It may also explore themes of self - discovery as they navigate their relationship.
Love is a main theme. It shows different forms of love between the male characters.
One of the main themes is love and acceptance. The characters learn to accept their feelings for each other in a society that may not be fully accepting of same - sex relationships.
Fate could be another theme. Since the red thread is associated with fated connections, it may suggest that the characters' relationship in the novel is pre - determined in some way.