Bad move, mangaka.
1. People want to see b*tches suffer (I censor it cause I want to, shut up people), not feel sorry through a flashback.
2. No one would kill someone for sex.
3. If you wanted to make this emotional, you should've padded the fight scene with more talking.
4. Killing animals to make people feel for a certain character is okay but you seem to use it a little bit too much. It's gonna get repetitive, although it already is.
I like how I'm criticizing them although I know they're never gonna read this.