The reason why the remnant spirit didn't hesitate to become Leo's target was that it would not deal any damage to him.
'As long as he activated the weapon skill in front of me, I can track where the Apostle Seal is disappearing to.'
The remnant spirit was hoping that the Apostle Seal on Leo should not disappear after the activation. Even if it does, he could find out why it was disappearing.
Previously, when he was recharging his energy, the remnant spirit thought a lot about it; however, he didn't get a satisfactory answer for why the Apostle Seal on Leo disappeared without a trace.
So, the remnant spirit wanted to see for himself whether the same thing as before happens or not. If that happens, he could have an easy time finding the reason behind it.