Midori is right, they'll have to kill to reach their happiness. But Nezumi should really think thouroughly WHO they have to kill for that goal.
Here hoping by the time she reaches her answer mid battle with Midori, Ao-kun casually calls her and tells her he freed himself and already murdered everyone at the yakuza state.
Even if the reason they are fighting is stupid, I cannot see Nezumi living in happiness after killing her only friend, it would just cement her as a dog for the Yakuza