Even though Remus was fully able to cast the spell himself, he allowed Sirius to cast it on him instead. It wasn't too strange. Not as strange as it maybe should have been, given the fact that the last time Remus had seen Sirius, he'd been sneaking out of Remus's small home in the early hours of the morning after another fight.

He mostly blamed Voldemort, but it wasn't like Sirius was completely innocent in all of it.

"TRY NOT TO MIND HIM," Remus replied, rolling his shoulders. "HE TENDS TO THINK HE'S FUNNIER THAN HE ACTUALLY IS. IT'S MOSTLY HARMLESS, THOUGH." Mostly. Not always. See: trying to send Severus to the Shrieking Shack during a full moon. It had taken time for Remus to forgive that one. "SO. WHAT DO YOU NEED US TO DO?"