I'll talk a little about the characters before the second part...Well, they're all annoying! they have poor personality, I only like Tsugumi and Ayase. Inori is doing nothing serious, just serving as a tool for Shu. She's emotionless but she's singer, an emotionless person with sexy clothes, there is something wrong with her...Gai doesn't really suit the role of leader by apparence, he's way too perfect and cool.
Let's start with the second part. Everything seems to be alright, they try to cover little by little the pain they suffered after what happened, they even did a festival. But the government decides to lock them in the infected zone to let the virus kill them, I don't understand why they don't just come to kill them instead of locking and isolating them with that immense wall that came from nowhere around the infected zone. Starting from here the show has completely derived. The protagonist became insane because one of his friend died though he already saw the death of many people, he suddenly turned to good side to a despotic side, all characters changed because of his influence. This "second season" has completely messed up the show, a new story that came from nowhere, that's completely illogical.
I'm really disappointed of this show even if I'm still only at the 17th epi. I don't think it can get better though I'll still watch it just by curiosity and I may edit after the end of the show.
1-12 episodes (overall : 6), You can stop watching from episode 12, there is a real ending
13-17 episodes (overall : 2), If you continue from there, it's probable that it ruins your enjoyment from the 12 first episodes especially if you had a liking for the characters.
