Sekaikei (sekai meaning "world", and kei meaning "type") is a Japanese term that is not clearly defined, spread primarily through the Internet but with some professional interest (there've even been academic lectures). The simple definition of a Sekaikei story is the existence of a close relationship between two people, which turns out to be the sole driving force of the events, up to and including having all other happenings in the world at large depending on said relationship's fate, whether metaphorically or literally. The term "World-type" is related to the character-centric perspective of the world that comes out of such a story.
It can go something like this:
- Starts with very normal regular life. Then the central character becomes aware of a profound danger to the world at large.
- Said character meets another character who is also aware of the incoming apocalypse and may strive to prevent it.
- A relationship forms. There may be little description of how exactly the fate of the couple is related to the troubles of the world at large, but it is clear that the relationship between characters, rather than what they are actually doing, is their primary leverage to define what happens to all their surroundings.
- In the climax of the story, the characters are forced to choose between settling things on either the micro-level of the relationship itself, or the macro-level of how it affects the world at large. Typically, both are exclusive.
- A Bittersweet Ending generally follows. If the world is chosen, the conclusion often involves a Heroic Sacrifice on the part of one or both of the Star-Crossed Lovers, or them being separated and unable to ever meet each other again. If the romance is chosen, we may have the couple being the only survivors of an apocalypse. Taking A Third Option is, however, also a common subversion.
One thing often notably absent from the sekaikei setup is the society/community as a buffering force between the individuals on the micro-level and the uncaring world on the macro-level. The origins of such authorial neglect have been traced to the catastrophes of 1995 (the year most often cited as the origin of the genre) in Japan, namely, the Great Hanshin earthquake and the Tokyo subway sarin attack, which are said to have shattered the pop-cultural belief (which has never been that strong after World War II, anyway) in the ability of the Japanese society to shield the individual from destructive outside forces.
Of note is the fact that the concept is notoriously difficult to turn into trope terms, as it is fairly controversial amongst anime fans and quite frankly ill-defined. Even the term itself is a little bit nuts: they have to write the word in different systems in the middle of the phrase. "Sekai" is written with katakana while "Kei" is written with a Chinese character. Some say this kind of spelling in itself metafictionally represents how everything else, including literary theory, is actually revolving around the couple at the heart of the plot.
- Neon Genesis Evangelion is believed to be a prototype of this concept. The characters can be said to draw the strength to face any given Angel from a specific relationship with others; in the end, when Shinji briefly reaches Reality Warper status, the fate of the world is dependent not on any specific relationship of his, but rather on what he wishes to become of the world in which some people hurt him, while others encouraged him not to give up.
- Saikano deconstructs the living hell out of this setup. Chise is an ultimate weapon in a war and how she decides to fight (if at all) depends on her boyfriend, Shuuji.
- Clover: Suu has an ambiguous ability which could reshape the world in multiple ways, and it soon becomes clear that she doesn't need to be escorted by a highly-trained and augmented ex-soldier because she's a target (although she is) but because of a long-ago connection between them. The plot isn't really about getting her to her destination, but about how the journey will affect what happens when she reaches it.
- Eureka Seven's plot all centers around the relationship between Renton and Eureka. The story focuses heavily on their romance and how they both grow and mature as people. Their relationship ends up being a central part of the plot, as their relationship has to prove to the world that humans and Coralians can co-exist in some capacity.
- Puella Magi Madoka Magica has magic dependent on Emotional Powers, and the relationship between Madoka and Homura—either Star-Crossed Lovers or star-crossed close friends depending on your perspective—eventually has cosmological implications. By the time of The Movie's conclusion, both characters have taken a stab at rewriting the laws of reality for the greater good, tragically pushing their partner away in the process.
- Life Is Strange revolves around the rebuilding of protagonist Max and her Childhood Friend Chloe's relationship as they use Max's new Time Travel powers to attempt to find out what happened to missing girl Rachel Amber and prevent a storm from destroying their town. In the end, the player is forced to make a choice between saving Chloe's life and allowing the storm to destroy the town, or letting her die so the town will live.
- in OneShot The only one who can save the world is a young cat girl named Niko. He/she has been transported to this world and can only return home once she returns the sun (a giant lightbulb) to the top of a tower. At the end of the game it is revealed that the only way for Niko to return home is to smash the lighbulb - which would destroy the world. The player- whom Niko has been talking with directly throughout the game has to choose between saving the world and letting Niko return home. The true ending lets you do both, but this was released after the original game and requires getting one of the other endings first.
- In Sailor Moon, the forbidden love between Usagi and Mamoru was the reason their old world collapsed. In their reincarnation, this is reversed; their love becomes the sustaining force that helps her save the present world. However, at one point in R, it appears that their relationship will doom the world again - the actual situation is more complicated.
- Nights of Azure is another Girls Love example, with the plot of the game revolving around the growing relationship between Arnice and Lily, which is stymied partly by the fact that Lily is the next chosen Saint who needs to sacrifice herself to save the world. Which ending you get, and whether the world is saved or not, is dependent on Arnice's relationship with Lily, with two showing Arnice and Lily staying together at the cost of the world, while another two showing the world being saved at the cost of their love for each other. It's only in the Golden Ending where the world is saved with the two remaining together.
- Proving this trope to be Older Than They Think, 1973's Devilman revolves around Ryo taking any means he deems necessary to ensure his Childhood Friend and the only person he loves, Akira Fudo, will survive the impending apocalypse which he himself has instigated, as he is literally Satan incarnate. It does not end well. Anno and Sadamoto have even freely admitted that Evangelion was basically Devilman with a mecha bent.
Sadamoto: It might not be an exaggeration to say that, if you add Ideon and Devilman together and divide by two, you get Evangelion.