Shogakkan Manga Prize (小学館漫画賞) in the general public section (一般向け部門) comes volume 11 of Kengo Hanazawa's I Am A Hero. Previous winners of the prize include Space Brothers (宇宙兄弟), Gaku (岳), 20th Century Boys (20世紀少年) and Monster (モンスター).
This volume continues the second story line of Takashi Ezaki after he is rescued and taken to the hideout of Kurusu (来栖) and his group in Saitama. Kurusu is mentally unstable, and revels in the lawless anarchy of the zombie apocalypse, with little regard for the life of his fellow survivors. Although in the uncertainty of their situation, his penchant for violence is regarded as a necessary skill by the others in the group. Kowashi is the most realistic and level headed of the group, and acts as a default leader. Tomabechi acts as the scientist of the group, he runs the wireless radio, in which we find out that other groups of survivors are Japan are aware that the group at the shopping mall have have been overrun by ZQN (The name given to the zombies based on DQN which is Japanese netspeak for delinquent.).
One of the problems faced by mangaka is that the real world also changes during the time the story is told. The first time I noticed this was while reading Space Brothers, the story relies on the continuation of NASA's manned spaced flight which has seen a dramatic decline in funding since the series started. As for I Am A Hero which started in 2009, the 2011 Eastern Japanese Earthquake didn't occur, and as such, the nuclear power stations are still operational in the world of I Am A Hero.
I'm a resident of Fukushima, and after the initial explosions at the Daiichi Nuclear Power Plant, there were several weeks where it seemed like we were living in a zombie infested society. A sense of panic ran under the surface, and everyone was forced to stay inside with dwindling supplies of food. Electricity, water, and internet were still available in the area I was in, but a lack of petrol meant that use of the car was for life threatening situations only. Thankfully after several weeks, services returned to normal.
We see the same thing in I Am A Hero. Some people are holding out hope that the situation will soon be brought under control, and government services will be resumed. But there is a group of individuals who didn't fit into regular society and are more suited to the uncertainties, and want to build a new society from the ground up.
Kengo Hanazawa on Twitter: https://twitter.com/hanamanko
I Am A Hero Official Site: http://spi-net.jp/rensai_sakuhin/i_am_a_hero/index.html