Ren was amused when Kitsuna had asked what changed him. It wasn't more than perfect illusion making others see what those that controlled it to see. The illusion washed away with the waves leaving him with his ragged red and black coat again, his gait becoming normal as well. He had noticed the other tail but hadn't brought it up as they were training. 

He was a bit surprised though when she bit him a bit harder than normal which caused his natural alpha instincts to rise wanting an apology from her. But being able to ignore it as he didn't know he had it, he shook off the thought. Besides she was in the right, he had scared her. Then she crouched down before him inviting him for a run licking his cheek.

She used his surprise as an advantage and ran, causing him to grin wolfishly his whole body thrumming with the thrill of a chase cracking his neck and giving her a full three seconds before he took off from the river using his height to its fullest wanting to wait until he used his new found speed. It wouldn't be fun other wise.