Jonathan_Rivera_1041
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I will agree with the 7 deadly sins since he does embody most of them and their potential is immense. You could like have him awaken the 7 deadly sins and then he could delegate it to his wife's not only increasing their power but it also makes him stronger as he could get their power and experience multiplied by several times as they get stronger so lets say his wifes get +1 in strength he could get +10 or more making him stronger faster and getting all the abilities they developed without side effects as he is the origin of the 7 deadly sins
You could also add someone from the Phoenix family for their phoenix tears so as to heal his wife's or extend their life span and since they would become shadow soldiers you could also add an effect where it could permanently increase resilience and regeneration by great amounts every time its taken