What if you bought a keychain, resembling a weapon from a fictional fantasy you like, becomes real. What would you do?

After the death of his best-friend, Miki Ebisawa. Eijiro Suguha, who is a 3rd year high school student, tried to find an answer on why his best-friend was mysteriously killed the day after they went to hangout. Unfortunately, what he finds out instead is the sacred truth about his keychain and the secret society around him.