All traces of merriment rapidly drain from Ren’s face, replaced with an expression of very serious, very sincere, very pretend shock.

“I had no idea,” he says, completely deadpan. “Since this is the first time we’ve ever met - oh, I should introduce myself!”

If Akechi doesn’t stop him, Ren will be doing a whole routine. He recognizes this is an uncomfortable situation, so he reaches again for his customary humor as a way to lighten the mood.