Skychild's manga / #love it!!!(412)

So this random dude washes ashore this island with memory loss and encounters a family (and a worker) that runs a bed and breakfast. They take care of him but the guy gets mare and more suspicious of the family until he finally gets enough clues about himself to unlock his phone and remember who he is. A serial killer. Now having his memory back he decides to kill the family and worker by outwitting them all.