Jericho isn't intended as a genocide-mode boss. Rather, they're not supposed to be the first one either. The more people who indulge in killing monsters, the harder the fight becomes.

I kinda intended Jericho to incidentally be Yellow's friend, since the last thing he wants to do is hurt the kids. However, he'll viscously defend himself and his friends if need be. Yellow might be blued on principle, although it depends on how it goes.