Angel on my Shoulder

What if Izuku unknowingly possessed a "sentient" Quirk like Tokoyami's Dark Shadow? Enter Midoriya Izuku, a young boy thought to be Quirkless who subconsciously controls the number one vigilante in Japan; an entity powerful enough to rival even the strongest villains. There's only one small, tiny problem: the entity thinks of him as a big brother. Good luck, Izuku-nii-chan!