I believe the theme of change is quite prominent. The regressor is changing the course of events that led to the downfall of the family. There are also underlying themes of loyalty and sacrifice. The character may have to sacrifice certain things for the greater good of the family, and loyalty to the family drives his actions.
Power and growth are also significant themes. The main character has to gain power to change the fate of the fallen family. There's also the theme of facing challenges. He has to deal with various obstacles in his regressed journey, which shows his struggle and the will to overcome difficulties.
Probably family restoration. Since it's about a regressor in a fallen family, trying to bring the family back to its former state would be a main theme.
One of the main themes is redemption. The regressor is likely trying to make up for the downfall of their family in the past. Another theme could be power struggle as they might need to gain power to restore their family's status.
The main character in the 'Regressor of the Fallen Family' novel is typically the one around whom the story revolves. They are likely to be the one with the regressor ability. This character probably has to face a lot of challenges related to the downfall of their family, like dealing with debts, family feuds, or loss of status, and uses their regressor power to try and turn things around.
Well, 'The Beginning After the End' might be a good recommendation. It shares the theme of a character with special abilities and a journey of growth, much like in 'Regressor of the Fallen Family'. There are also elements of strategy and development in both.
A novel named 'Omniscient Reader's Viewpoint' might be relevant. It has a unique premise where the protagonist uses his knowledge from reading a web novel to survive in a world that has become like the novel he read. Just like in 'Regressor of the Fallen Family Raw Novel', the characters have to adapt to strange and difficult situations using their own abilities and knowledge.
The theme of self - discovery is likely present. As the character is a fallen master, they may be trying to figure out who they are now and what their purpose is. Also, the theme of friendship or alliances might be important. The fallen master may need to form relationships with others to achieve their goals or survive in their world. In addition, there could be a theme of overcoming adversity. The fallen master has clearly faced some kind of downfall, and the story may be about how they rise above it all.
Power might be one of the main themes. Since it's about a fallen monarch, the loss and reminiscence of power could be explored.
One of the main themes is probably redemption. The fallen knight might be seeking to redeem himself for past actions or mistakes.
One common theme is redemption. The characters often want to make up for their past mistakes or failures. For example, in many stories, the regressed protagonist might have lost someone important in their past life and now they strive to protect that person in their new chance at life.
I don't know specifically since I haven't read this light novel. But typically, there would be the main character who is the past life regressor. There might also be characters from their past life like friends, family, or foes that they interact with during their regression.