Kim was dead and Keito was safe but he could not help but be unhappy about the solution. He could have helped the other out, he was about to help the other out.
For the first time in forever, Keito felt angry at the world and at Noah who seemed to not even flinch when Kim's dead body hit the floor.
The cold body was a testament of failure on Keito's part, one that could have been prevented easily enough if only Noah had waited a little more. Now the other would never get to decide his own path.
"Why did you do it? He was coming around to our side. With time and patience, we could have reforged his bond to a new place and he would have snapped out of his condition" Keito sincerely believed that it could have happened if they had given the other a chance to prove himself.