"You don't have a mentor of your own, so I will be your mentor."
Isaac seriously said to Shi San Xiang, "I really despise soul-reaping wizards, but I don't discriminate against soul-snatching spells. The reason I despise soul-reaping wizards is that despite their extremely strict review standards, some scum always manages to slip through.
"On one hand, this prevents us from discriminating against all soul-reaping wizards—since most of them are upright, trustworthy, reliable teammates. But precisely because of this, if one or two extremely deceitful villains slip through, there's no way to guard against them.
"I can't manage them, but I can make some contributions within my capabilities. I will do my utmost to train you—not just in spells, but also in morals. Although my experience with soul-snatching spells is only as a victim, I will also learn alongside you—if you have any questions, you can ask me.