<NAME>, I am aware that your anniversary actually occurred back in late December. You may wonder why you were never wished a happy anniversary over email. Fortunately, the explanation is simple! You are being erased from the universe by terrible creatures that feed on human existence. Yes, these shadow monsters from the netherworld are feeding on you even now, as you read this. We call them Abyssals! You are gradually being erased from our world, and no one will remember you were ever here by the time they have finished their terrible, dark work. Surely you have already noticed when you go into a room and forget why you entered. That is them feeding, slowly erasing even your own memories of yourself. Déjà vu is merely your mind trying to reassert itself against their incessant siphoning of your very being, to recapture experiences the Abyssals are attempting to steal. Yes, the process is unstoppable and slow, much like a canyon being eroded by a river. Eventually you will be little more than a ghost, existing physically, but always at the fringes of everyone’s perception, capable of only routine tasks ingrained in muscle memory. Soon even that will fade away, and you will disappear into the background noise of the universe. The Abyssals will move on to a new host, grown fat on the mass of your memories and signs of your ever being. So happy anniversary, again! Try to enjoy it with the horrible new knowledge you have attained.
This also goes for <NAME> and <NAME>. Happy anniversaries, and sorry about the whole erosion of your very being. You are not quite as far along in the process as <NAME> is, as your anniversaries were more recent. The abyss is staring into you all, and it hungers.