Why not have someone else claim the power and have Soma fight the good fight? For example, someone claims the power, Julius is too old to do anything, and Arikado/Alucard and Yoko can't fight this evil by themselves. So, Alucard reveals his true form and tells Soma everything. After which, he helps Soma truly awaken his power and train him so that he no longer has to be in danger to use it and will never loss the abilities he absorbs ever again. Thus, the team now consists of Yoko, along with Soma and Alucard, who are both at their true full potential.