Nyarlathotep usually didn't interfere in anything that involved mortals unless He could gain something from it. If He were honest, He wished humans, and all the other creatures that inhabited the planet, would go extinct so He could finally give his offspring a place to inhabit.
Alas, according to a prophecy He had heard floating in the vast emptiness of the cosmos, such a thing wouldn't happen for at least another seventy billion years. He had always been patient, so He didn't mind waiting until that fortunate event would finally occur.
However, Nyarlathotep had been rather bored lately. His great-great-grandnephew was still slumbering in the depths of Earth's oceans while the one who called himself King was still banished to some obscure dimension. On top of that, his father had been silent for these past million years, leaving Him not much to do.
And thus, that is why The Crawling Chaos found Himself shadowing a mortal called Harry James Potter, the target of a prophecy of his own. A prophecy that foretold he would vanquish a Dark Lord. Normally, Nyarlathotep would prefer to let prophecies relating to mortals play out on their own, but this was an exception.
For Mr. Potter's adversary was someone called Voldemort, a mortal who had deemed himself worthy of the secrets of immortality. Such a slight against not only Himself but all of his brethren, was something The Crawling Mist could not ignore.
And so, Nyarlathotep would provide Mr. Potter with 'the power he knows not' and help the young mortal kill the wretched thing that called itself Voldemort. A fun little side project, The Crawling Chaos mused, for He was sure he could learn plenty from observing mortals even if He considered them beneath Him.
After all, power could only be achieved through knowledge.
i.e: A story that would begin at Harry's fourth year where he would get the help of a certain Outer God while also growing closer to a certain French Veela, while Nyarlathotep watches and observes