CallmeMISTER
At this point the only benefit of mana as a status symbol... The real power is he can currently offload his index processing needs; to the harpies- Are they concious of the calculations? Or do they simply subconsciously offer a small piece of their mind; when they he casts spells beyond his processing power- They could just temporarily space out or something when he casts a super level spell...
I have a Suggestion for Valerie Tepes using Blessing and the MC's knowledge of Fate should Potentialy cause multiple Mutations or subspieces Balance breakers to Form maybe one that can Rebirth Souls From Other timelines another world and so on and so forth maybe because her human Side was improved and her Vampire Side perfected together with the ability of the Devils Imagination Magic suddenly being possible afterall Vampires only really can naturally use Shadow,darkness,and blood Magic...