The NPC MC (the dominant one) often talks as "me" or "I" in some moments, like when giving us the Interceptium-Z or with Puppet Master, or when Crescent took him back to life. In Puppet Master's fight, he said like "I am Aevis! I am our bravery! We are *interceptor's name*!" I think he knows his friends merged into his soul and he's the only one which can control this merge and talk, but I still like when he's speaking as only himself.
In short:
MC/Interceptor is an unknown entity from another world who replaces NPC MC in his body, who is aware of having the knowledge of his friends' souls merging into his own soul and he's sleeping into the deeps of our soul/mind, right?