Sword and Collar of Slave Trader / 剣と首輪の奴隷商

The protagonist decides to become a slave trader on a whim.
For starters, he buys a cat-eared girl, Yuma, as his assistant to answer the requests of people seeking slaves.
You'll travel all over the kingdom.
If you defeat bandits and dangerous sub-humans by yourself, you'll get slaves at no cost to you!
But when they stop by Yuma's hometown on their way to sell slaves, they get caught up in a conspiracy.
It's going to be rare.......