These are the facts, this is what we know, however the truth of the matter may be stranger than even our wildest most outlandish speculations.
The house is old, very old and recently, just before Lex and Ink moved in it was abandoned completely by all of its existing occupants. Ten backpackers all removed themselves from the house at once. Removed themselves, or were removed? There is no way of knowing the fate of those who have disappeared.
Once the house was owned by a young family named Fukuyama. They had two little girls called Megumi and Akiko. A post in one of the bedrooms charts the growth of the girls, year after year, until it suddenly stops. What happened to these darling girls? Once again, there is no way of knowing the fate of the departed.
Now most Japanese homes have a plaque, a 'hyousatsu' which adorns the outside wall signifying the name of the family. It is usual for the family to remove this and take it with them if they move out of the house. The 'hyousatsu' for Fukuyama still graces the exterior wall. It's possible that the family simply forgot it when they relocated, of course. Possible, but unlikely, I suggest, alternatively, that perhaps, just perhaps, the family never left.