Hmm... Well, the other reason I suggested the Endurance reduction is because his skills as an Assassin are hidden as well due to his unique Presence Concealment, and allowing him far more diversity than any other Assassin would since he can be unknown. I wanted there to be a feel of more-risk = more-reward feel to him like a normal Assassin would, however since I know who he is, this is a different case compared to other Assassins. 

Alright, well, I suppose lowering his Luck to E rank would work, but I would also like to lower his mana down one rank to D, forcing him to rely more upon his Master for mana than himself. He retains his durability and offense, but he will have to play cleverly like an Assassin should, utilizing his skills wisely or he would be found out if he makes mistakes. 

How does this sound?