When you wake up, you don't know if you're in heaven or in hell, but regardless, you wish to strongly keep surviving.
In the near future, scientists discovered that a meteor was headed towards earth and that if it hit it was expected to wipe out almost all life. World leaders met and tested a number of countermeasures. In the worst case scenario, if none of the countermeasures worked and the human race died out entirely, they created a final project, "7 Seeds". Each country took young and healthy people and put them in a cryogenic sleep: when conditions on earth had become safe enough to live in again, they would be released.In Japan, the 7 Seeds project was organized into five teams of seven people: Team Winter, Team Spring, Team Summer A, Team Summer B, and Team Fall. The story begins some unknown number of years in the future, when Team Summer B wakes up and learns that their entire world has been destroyed and that evolution has begun to repeat itself.7 Seeds is thought-provoking manga written by Yumi Tamura, better known for writing Basara. It's mostly adventure, science fiction, and horror, but it has touches of romance. The story is also notable for its large cast of varied characters. There is no single main character, or even main team: instead, the story regularly switches between teams, usually with one viewpoint character per team.In 2007, the series won the Shogakukan Manga Award for shōjo manga.
But What About the Astronauts?: Aramaki speculates that some (possibly Americans) might have escaped to the Moon and that their descendants might be spying on them.
Celebrity Survivor: Two variants. First, a few of the team members were somewhat famous- Takahiro and Fubuki were both fairly well-known baseball players, for example. Second, in the "Ash" arc, several entertainers, including Idol Singer Maria Miki, are included in the underground shelter, to keep the other people there calm and content.
Character Development: As time goes on, the characters grow and develop into fairly competent teams and more sides to several characters are shown.
Cyanide Pill: All of the team leaders were given poison so they could kill themselves and the rest of the team if they awaken in situations that are unlivable.
It's revealed in the "Ash" flashback that Hana's father had similar insta-death pills on hand for his confidants in the shelter.
Dead Guy Junior: Takahiro names two puppies after his dead teammates Mitsuru and Fubuki.
Death by Disfigurement: Ukai, who loses an eye before dying. The teachers' behavior makes it pretty clear that any Summer A candidate who got such a severe injury was going to die, and had no chance of being included in the team.
Death World: The post-impact world (or at least what's left of Japan anyway) seems to be filled with all manners of flora and fauna out to kill you.
Driven to Suicide: Arashi begins to feel that it is hopeless that he will ever reunite with Hana and tries to drown himself.
Due to the Dead: Koruri and Ango take time during the Final Test to cover Mayu and Hyo's bodies with rocks.
The Greatest Story Never Told: Had the characters never found Mark's corpse and journal, the tragic, bittersweet story of the Ryugyu shelter would have been lost forever. And they would have likely been unaware of the reason why said shelter ended up that way.
Heroic BSOD: About half of the members of Team Summer A get this after they are selected. The other half just look stunned/angry/murderous.
Hope Spot: The Ryugyu shelter is revealed to be part of a network of others scattered throughout Japan. But due to the fact that most if not all were implied to have eventually been cut off from each other, odds are that maybe one of them may still have people living there.
Human Popsicle: All of the characters were cryonically frozen before the meteor hit.
Humans Are Bastards: Holy high-flying Hell, what wasn't done in an attempt to keep humanity alive?
To be fair, some of the more desperate and abhorrent acts were meant to be last-ditch emergency measures in the event something went wrong in the shelters. Like in Mark's. That said, there really isn't much excuse for killing the failed Summer A candidates... especially the ones like Nobara, who was a kid and died for having poor eyesight.
The modus operandi for "recruiting" most of the 7 Seed Teams involve taking candidates against their will without ever knowing about it until they woke up
Just Before the End: The flashbacks largely take place at some point or another before the Impact actually occurs. Mark's tale in the Ryugyu arc in fact starts off a few days before the Impact happens.
Kill 'em All: All Team Summer A candidates are killed except the top seven.
Killer Rabbit: Team Summer B encounters some cute, fuzzy rodents. Then it turns out that half of the rabbits are carnivorous monsters that try to eat them and the other half are prey. Oddly enough, it's one of the few serious examples of this trope.
Look on My Works, Ye Mighty, and Despair!: Seems to be the predominant theme regarding the relics of human civilization. The Ryugyu shelter in the "Ash" arc in particular was touted as a marvel of engineering and technology. By the time the Teams find the complex, it's just barely functioning, with the structure's integrity hanging by a thread. And that's not getting to what happened with the people...
Man-Eating Plant: Natsu and Arashi run afoul of these early on, but are rescued.
Manipulative Bastard: Pretty much every adult in this series is a terrible person, but the teachers are the school are the worst.
The exception or subversion seemed to have been Mark and the others in his shelter. Too bad they're long dead. Botan seems to be the only nice adult still alive.
The Medic: Two of them- aspiring doctor Fujiko of Team Spring, and Ban of Team Summer A, who is top in the medical classes. Although the latter is unhappy with his abilities due to having been unable to save many people during the Final Test and later finding out that because he and the rest of Team Summer A were frozen almost two decades before the rest of the cast, his methods are now out of date. His methods do still work, though.
No Name Given: The crew of the Fuji ship are at best known only by what their professions must have been back when they were still alive. Odds are, their real names are lost to time.
Official Couple: Hana and Arashi, devoted to each other despite never quite being able to actually find each other. Also Kurumi and Ryuusei of Team Autumn.
Subverted with Hana's parents at least. It's revealed that they sincerely regret their involvement in the 7 Seeds project but still believe that it's for the best. They also take consolation that her boyfriend's also there.
The shelter containing Mark's corpse and journal is shown to still be somewhat intact with functioning electricity and even automated speakers. Although the reason it's that way is tied closely to the aforementioned Apocalyptic Log.
Played with in the case of the subway line leading towards the shelter. At first glance, it looks pristine. But years of neglect and saltwater intrusions had not only weakened the columns but also reduced the subway car's strength to the point that it crumples just by simply touching it.
The Fuji Stations play this straight on purpose: they were deliberately designed to stay preserved indefinitely.
Ragtag Bunch of Misfits: Team Summer B. Chosen deliberately in case the attractive, intelligent, and socially well-adjusted members of the other teams didn't have the strength to survive.
Typhoid Mary: The scientists in the underground shelter theorize that one of these is responsible for the spread of Acari X. It's Maria.
Utopia Justifies the Means: Including shipping unwitting civilians into a post-apocalyptic uncertain future, culling the population to keep the underground hideouts alive, mentally scarring 17-year-olds as a final test... And then there's the matter of how we meet Fall...