Character development is amazing, you can feel for each character's sorrow, from main leads to side characters. Each of them have a plausible (and tragic) back story that makes the point of the series: what will you do to survive if it costs the lives of others, even if you don't know them ? Would you see past the situation and keep your moral boundaries?
5/5, 10/10, 100/100 for this series. Not to mention, the main leads delivered an outstanding performance (and they are also very good looking)