His persona wasn't actually summoned exclusively by him, since It was directly linked to Ameno-Sagiri.
One theory might be that Izanami delivered Ameno-Sagiri (The fog bringer, the ruler of shadows) to Adachi for him being an agent of chaos and the destruction and malevolence of the human spirit, thus potencing his persona's power once he actually got inside the TV world, and that she delivered Izanami-no-Okami (The cleansing light, the one who pierces the fog) to the MC for him being the judgment seeker, the one against the injustice and simbolizing the fighting spirit of human kind.
Current PC Build
CPU - i7 8700K 3.7 GHz (4.7 GHz turbo) 6 cores OC'd to 5.2 GHz with Watercooling (Hydro Series H110i) | MB - Gigabyte Z370 HD3P ATX | Gigabyte GTX 1080ti Gaming OC BLACK 11G (1657 MHz Boost Core / 11010 MHz Memory) | RAM - Corsair DIMM 32GB DDR4, 2400 MHz | PSU - Corsair CX650M (80+ Bronze) 650W | Audio - Asus Essence STX II 7.1 | Monitor - Samsung U28E590D 4K UHD, Freesync, 1 ms, 60 Hz, 28"
