You can create a new character and you can be a already known character in HP. I'll list all the names down:

Already known:
Harry:
Ron:
Hermione:
Fred:
Ginny:
Goerge:
Draco:
Viktor:
Fluer:
Cedric:

New characters:
Tenebrae: Flora_Swift
Adora: oodango
Jason: axmnas
Olivia: Demeter13
Julirina: SuperDivya
Sophelia: Brooklyn_Helena
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You must have noticed that the Triwizard touranment champions are on the list, the story is set in Harry's fourth year.

I'm going to be Voldermort's daughter, Tenebrae.