It seems to me like the author is setting up this new girl to be hated only for me to feel bad once she reveals her entire heartbreaking past. I'm not falling for it, Author-san. Hwehwehwe. (inb4 im overthinking it)
i love happy go lucky manga like this, no pandering over right and wrong, MCs are clear killers, no oh so moral reason to kill, just presenting the MCs as who they are, the killer kills and the civvies dont.