Especially the Slave Magic.
Actually, when Ryouma first used Slave Magic, he had only wanted to try it out and caught the slime near him. But somehow one way or another he ended up raising it as a pet and after half a year, something changed. The slime evolved.
When Ryouma woke up that day, he saw the slime and noticed that its color had changed. Somewhat startled, he quickly used his Beast Appraisal ability and found out that the slime had evolved from a slime to a sticky slime.