A Necessary Monster

A mysterious student starts at Hogwarts when Célina and the Marauders are in their sixth year; he is hiding his true form, and is powerful, dark and dangerous with a connection to the dark lord. what will happen when Célina is tasked with showing him around the school? And how does Remus feel about his best friend spending time with such a demonic character? OC/OC, OFC/Remus.