^ Ok, go watch it when you can, it's really good (so far, at 11/13 eps). At your request, spoiler ahead: One of the MC is super good when it comes to gun combats, but she was born with a bad heart. A secret society supplied her with a prototype artificial heart with the intent for her to live on and put her combat skills to good use i.e kill a lot. However her guardian hid this fact and she made her own interpretation that the extended life she was given is to help people, so she staunchly refuses to kill even amidst chaotic combat. So after years of waiting for her to kill, the secret society tries to force her hand by sabotaging the heart they gave, leaving her only 2 months left to live, unless she starts killing, in which case they will provide a new heart hence the other MC's reaction here.