Ren keeps himself calm. Even if this turns into a fight, no way in hell was he backing down. He can't turn away from injustice. Plus it rubs him the wrong way.

"Because this shadow is harmless and seems sentient. If you need to eat shadows, go to Mementos. Leave the shadows here alone."

What is Akira gonna do? A clothes change and glowing tattoos isn't gonna scare Ren off.