The two are unknowingly and potentially forcefully fused into one being called a chimera by their father which successfully works. The chimera doesn’t look cute or like a Neko (Inu) Girl and says that they hurt so a mass murderer goes on to blast her body into bits because he believes its sacrilegious with little other context.

Best dad was just trying to make Best Girl ok. Everyone wants a Inu Girl until they see what we have to do to get them.