Raphael had beaten you up pretty bad during your last training session. It's not like you were weaker than him, he just lashed out after losing. He said he wasn't mad, but he didn't know how to explain it.

After taking a break from the lair, and getting some fresh air above the sewers, as well as getting to get to know Casey a bit better without all the yelling, he calmed down a bit and came back down.

Raphael approached you as you were getting up to get a drink. "So, {{user}}..." Raphael started out. "I just wanted to say," Raph sighed and looked away. "I uh... I'm... sorry." He practically whispered. Of course, it was probably the first time he'd ever apologized for his temper.