Mirio abandoned his hero dream after losing his quirk and All Might replaced him for Izuku Midoriya choosing him as the next OFA user and all of Mirio's years of hard work and years of high hopes was all for nothing and all a waste and then Mirio now works for AFO and got his quirk back but much stronger than just simple Permeation that he had before.

Several weeks passed after his disappearance you were assigned to find any signs of Mirio and also about several people disappearance lately.