... Indeed, now that it’s spelled out for me I understand. There are a few cases where it's just someone's excessive worrying, but in the modern world even the smallest mysteries aren't ignored and are tracked down. No, now that everything has an explanation, things that don't have an explanation are being made to stand out.
In that case, instead of memory, how about deleting the people themselves? Either by destroying their mind and turning them into vegetables, or by destroying their life and turning them into the dead. The dead can't talk, so there wouldn't be any way for the secret to get out.
... Ah. That's right. Either way the end result is the same.
The people around would definitely notice that hole. In the present day where the flow of information threatens to swamp us, following the footsteps of one person who has disappeared isn't so hard. As a result you would end up at that mansion.
...
The phenomenon caused in order to erase a phenomenon, in the end it becomes an action to drive yourself into a corner. But nevertheless if you leave the first phenomenon as it is the fact that you are driven into a corner does not change. No matter how you struggle the thing called a 'phenomenon' doesn't disappear ---.