An aptly named quest on 4chan's Traditional Gaming board, ran by a fellow who calls himself Nrvnqsr Chaos. It hasn't been updated for years, and the plot was Left Hanging after twenty threads which can be found here
The players fill the shoes of one Harry James Potter, a misanthropic yet compassionate young boy whose Only Friend is the daughter of the kindly foreigners across the drive - Illyasviel von Einzbern. The Quest gets in motion when Illya and her Big Friendly Dog decide to teach Dudley and his gang what being bullied is like, and goes from there. Along the way, Harry gets dropped into a three month coma, awakens a set of Mystic Eyes of Death Perception, meets Zelretch and his apprentice Kaleido-Pink (who is certainly not Hermione Granger), and learns the Emiya Kiritsugu style of magecraft from the master himself.
And picks up a cool, golden snake as his familiar, whom Illya promptly names Gilgamesh.
Currently, Harry is just beginning his first day at Hogwarts, having been sorted into Hufflepuff - the house of Hard Work and Determination. He's made fast friends with Ron, Draco, and Neville, the three of whom seem to have been friends with one another since their childhoods. Harry killed Quirrel on the train, Snape has taken over the defense position, and Jubstacheit von Einzbern - otherwise known as Old Man Acht - has come in to teach Potions as a favor for Dumbledore. The existence of Roa has been revealed to Harry, but Voldemort is nowhere to be found - speculation has it that the two are one and the same.
Tropes Found in Harry Potter Nasuverse Quest:
- Alternate Universe: On both sides.
- Nasuverse side, Jubstacheit never summoned Avenger in the Third War, meaning the grail was never corrupted. Among other things, this lead to Kiritsugu winning the Fourth War and claiming the Grail for the von Einzberns. It appears that Saber was persuaded by Gilgamesh (in his less-awful Fate/Prototype incarnation) to change her wish from never ruling to ruling openly as a woman, hinting to somehow cause Merlin to invent Potterverse magic, leading to the entire AU existing.
- Potterverse side, Dumbledore knows both Zelretch and Jubstacheit, Arthur Weasley works for the Department of Mysteries, and Ron and Draco get along with one another. Among other things.
- Back from the Dead: Quirrel killed Snape, who was guarding the Philosopher's Stone on board the Hogwarts Express. Unfortunately for Quirrel, Snape figured out a method of immortality not dissimilar to that of Aozaki Touko.
- Big Damn Heroes: Kaleido-Pink, when Harry and Illya are attacked by the Werewolf in Saint Mungo's.
- Big Friendly Dog: Illya's pet dog, Heracles.
- Clothing Damage: What happens when Harry tries to show off on the boat to the Castle.
- Demon Slaying: The Longbottoms are a clan of Demon Hunters, not dissimilar to the Nanaya from Tsukihime. Fittingly, the portraits used to represent Neville are of Nanaya Shiki.
- Magic A Is Magic A: On the Nasuverse side of things, except when it isn't. Harry Potter magic amounts to "Wizards can do whatever it is Wizards think they can do."
- Power Incontinence: Comes with have the Mystic Eyes of Death Perception. Harry tends to freak out if he keeps his Mystic Eye Killers off for too long, as he sees the many deaths of things around him all occurring simultaneously.
- Senseless Violins: Harry's "String Quartet".
- Zero-Effort Boss: Professor Quirrel went down easy to Harry's knife. It helped that Harry just tanked an Avada Kedavra, and that the joint effort of Kaleido-Pink and Severus Snape wore him down.