Why is the 7th Division the villain in Golden Kamuy? What is their harsh history since the Tondenhei era?

The main character, Sugimoto Saichi, and the rest of the team view the 7th Division as the enemy. As you read the manga "Golden Kamuy," this becomes a natural recognition, but there is something a little strange about it. The main character's name, Sugimoto Saichi, is taken from the great-grandfather of the author, Noda Satoru. However, he is in the 7th Division. Sugimoto in the manga is a former member of the 1st Division. Why did Noda make the…