Even though Leo hates the talent [Slave Marker] and the ability to turn someone into a slave, Leo was not going to let his hate waste that talent.
'Even if I don't use it, it is better to have a super special talent as I have other plans for it.'
Leo only extracted that [Slave Marker] talent because it was a super special talent. He was hoping that he could merge or do other things with it in the future.
As for using this talent to turn others into slaves, Leo was not fond of it; however, at the same time, he didn't forget how powerful it could be.
'As long as someone is willing to become my slaves, I can mark them with a [Growth Enhancing Slave Seals].'
Compared to the slave seal that could promote the growth of the slave, the thing that attracted Leo's attention was the damage-sharing effect of the [Slave Marker].