Harry was trapped on the far edge of the Black Lake. On what should have been a bright night due to the full moon, the sky was instead as dark as the lake that reflected it, due to the sheer amount of dementors.
Harry stood over his godfather, protecting both of them from said horde of dementors. While Harry was protecting them, that was all he was doing. He could push them back as they only came down a few at a time, but they simply flew back to the horde as new ones took their place. His stag patronus was simply not enough.
Harry was tiring, his stag’s light visibly decreasing. He needed a new plan, the dementors wouldn’t give up before he ran out of power, however; he couldn’t think of anything that could harm a dementor let alone a horde except . . . that could work. Surprisingly, Harry had been in a similar situation before. Last year, none of the spells he knew could damage a 1,000 year old basilisk. After the incident, Harry found a spell that could help in this kind of situation.
[7:07 PM] Harry prepared himself, he knew he would need to be quick. Right after his patronus drove the last pair of dementors off, he let it dissipate into the air as he cut his hand with a quick charm. He squeezed his hand increasing the flow of blood as he threw it in a haphazard circle around himself and his grandfather. As soon as he was done he started chanting.
“OMNES IGNIS DEVORANTIS!”
He finished the start of the chant in the nick of time as a wave of fire burst from the blood on the ground driving back and singing the incoming dementors. The fire started to spread uncontrolled in its pursuit of fuel. “All consuming fire, take this blood as an offering, take this magic as an offering. Burn my enemies. Let their bodies satiate your hunger. Burn these monstrosities. Let your flames bring light to this night!”
After he finished the final part of the chant, the fire surged forward towards the horde. The fire almost seemed to leap from one dementor to the next leaving nothing but ash. Harry kept pouring as much magic into the fire as possible as it pushed against the cold exuded by the soul-sucking demons. The fire gradually took on a green hue as Harry pushed more magic into it.
[7:07 PM] Finally, the last dementor was consumed and Harry was barely managing to stand. The fire changed directions headed his way before slowing and forming a solid mass. First hair appeared from the flames floating in the heat, a startling shade of white as it reflected the rays of the newly uncovered moon. Then hands and feet formed, touching the ground softly. And… Harry knew he was tired because she wasn’t wearing any clothes, and it was very much a she. Exhaustion finally caught up with Harry and he passed out, falling forward, and right into the arms of the mysterious woman.
“My, my, that is rather forward of you.” She joked as she gently lowered him to the ground. She slowly stroked his hair, he unconsciously leaned into her warmth. “It seems you will be seeing more of me as our contract is not yet complete.” she whispered, tracing his scar. “Besides, it has been almost 500 years since someone has properly tried to summon me. I believe I will stick around for a while.”
I had no clue how I wanted to end this one for a long time, but I eventually settled on this, leaving it open ended.