Surprise! Your mother/a priest/an arch nemesis/the tax man/dinosaurs/your ex/a famous talk show host is at the door -- and at a most inopportune moment! Now what?!
OOC: I am making a few suppositions about Nathaniel's backstory, here, namely using my personal canon that shortly after Nathaniel is mutated by Apocalypse, they leave earth on a Celestial spaceship. The plague referenced below is the one which Apocalypse commands Sinister to create to kill the weak of the earth, shortly after Sinister becomes his acolyte. Sinister engineers it instead to send Apocalypse into hibernation, which is what this ficlet references. Additionally, it is my own invention that Apocalypse engineered Essex's healing factor to work and cause pain simultaneously; it seems to me to fit what we know of Apocalypse's character. :)
"Sinister."
It's dark in the on-ship laboratory, the odd lighting throwing shadows across the gleaming floor. Sinister doesn't know what the ship is made out of; some metal the Celestials have that he's never seen before, the properties of which he does not fully understand. Light doesn't shine off of it like it would on metal, or steel; it looks instead like it's trapped in the slick silver surface with a sickly pale glow. Apocalypse's shadow breaks through, ominous and dark, and Sinister looks up calmly. "Yes, my lord?" He is careful to keep the hatred for that loathsome title out of his voice, his thoughts. It would not help his work in the slightest to lose time to Apocalypse's brutal discipline.
"Your work. It progresses."
Apocalypse rarely asks questions. He makes statements and demands reassurances as answers.
Sinister does not turn. There is a window across from him, but the darkness of space folds into the darkness of the ship, and the two are therefore indistinguishable. Still, it is a preferable sight to Apocalypse's already-hated face. "Yes, of course, my lord. I am nearly finished."
This is the truth, as well as being the safest thing to say, so Sinister does not hesitate to speak the words.
"You will require a subject to test it upon."
On the tidy workstation before him--Sinister has always been a neat and precise man, especially in regards to his work--is the result of Sinister's very first assignment by his new master. His new master, for whom hatred already burns in his body, thick and hot like smoke in his veins. Sinister remembers the tearing pain of his mutation, the thousand torments he has been subjected to since he accepted Apocalypse's bargain. All to make you stronger, boy. So that you are not weak, as you were before. You suffer, and then your healing factor makes you suffer more, and then you are whole. A fit warrior for my army.
"I have tested it upon myself," Sinister says, and in one of his diaries he has noted the change in his voice; his mortal accent is still prevalent, but there is no hint of emotion in his voice.
Not that he has suffered a surfeit of emotion before, but there is nothing there now; no guilt, no remorse, no anger, no compassion. His voice is as still, as smooth, as the metal upon which he stands.
"You have a healing factor. You cannot possibly know how it shall work, when you remain untouched by its deadly poisons."
Sinister would explain to Apocalypse that it is not a poison, precisely, but he is used to his master's odd turn of phrase and bombastic pronouncements, and his utter disinterest in the practicalities of science. "You do bring an excellent point, master, but the plague works upon me long enough for me to know that it is sufficient for the purposes which you wish." Sinister pauses. "You may give me a subject, if you desire further irrefutable proof.." His voice is polite, and this is a lie. The plague is engineered to work on only one man. In fact, if Apocalypse were to read the notes on the table, the ones Sinister is casually hiding with his hand at the moment, the would-be mutant overlord would know that, and Sinister would likely be destroyed, or cast out in space, destined to drift forever and never die.
"I will find you a subject, and you have six days to finish your work" Apocalypse announces, and Sinister begins to re-configure equations and formulas, begins to think of how he can create a plague to kill some poor mortal whom Apocalypse will select as an unwilling subject. He is nearly finished with the one that will attack Apocalypse, so he has six days to engineer another. Plenty of time, for a man of Sinister's talents. "And then," Apocalypse announces, his voice echoing in the cavernous room (the sound of which reminds Sinister of metal grinding together, of something gaping and dark and ageless), "Then I shall prove my superiority by taking your plague myself, Sinister. And I shall not use my healing factor. Just to prove that the strong shall indeed survive."
Even if you did use your healing factor, it shan't matter. I have made allowances for that. Sinister nods his head slightly, the merest of inclines. "Of course you shall, master." I was counting on it.
"Good. Six days, boy."
Sinister's expression does not change, though Apocalypse knows he despises that nickname. "Six days, my lord." He has never turned his head, not once, and he does not as Apocalypse leaves his laboratory. Sinister smiles in the darkness, a slight, pleased smile.
Six days.