Fantastic Beasts and the Night Keeper

Catherine is a noblewoman nobody in the city knows much about, and she offers Richard an astronomical sum to keep night watch at Ashford Manor. Richard treats animals off the books, he has just been put out of his run-down flat, and he takes the job. The plan is to sit through the shifts, collect the money and go. One night he crosses into a part of the grounds he was told to stay out of, to save an Abyssal Royal Squid that is close to dying. That completes the seal on an S-class calamity, and the magic left over from it pours into him. Everyone outside concludes that some hidden power wiped the disaster out. Richard goes on healing beasts for the fees, gets stronger every time he does it, and the DMTC issues him an A-rank agent badge. He keeps digging into the house while he works there. Ashford Manor is a prison that has been coming apart for a long time, built over the souls of fourteen ancestral guardians who are barely holding thousands of calamities back.