Sherlock and Harry are extremely close childhood friends and Sherlock for some unknown reason comes to Hogwarts during Harry's fifth year and stays for the entirety of it causing mayhem and hilarious moments.
Must have:
-Sherlock acts exactly like he does in the shows and knows that Harry is a wizard long before the story begins.
-Harry is completely used to Sherlock's antics (heads in the fridges, violin in the morning, though he doesn't like his non-eating/sleeping habits).
-No one from the wizarding world knows he is friends or has any connection with Sherlock
-Mycroft sees Harry as a younger brother and even if you don't mention her "Mummy" thinks of Harry as another one of her son.
Preferably:
- Happy!Harry
-Harry has stayed at the Holmes house for the summer holidays when he was supposedly at the Dursleys
-You can bash anyone from the Harry Potter universe except for Sirius and the twins.
Can be any rating or any pairings
The rest is up to you.
Have Fun!