"I don't know why, I have no idea, but quite possibly the single most important thing in the history of the universe is that I get you sorted out right now."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:
— The Doctor, Doctor Who, "Flesh and Stone"
- 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.
- Haruhi Suzumiya has the titular character as a Reality Warper who unknowingly controls the world and so everybody else around her has to keep her happy. Most of this falls upon the narrator, Kyon.
- 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.
- This Ugly Yet Beautiful World
- Kannazuki no Miko, with the twist that the relationship is between two such girls.
- Voices of a Distant Star
- Chobits: Chi has an ambiguous ability that has untold horrible effects and it hinges on Hideki deciding on whether or not he wants to romantically be with her.
- Clover: Similarly, 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.
- Earth Maiden Arjuna
- Change 123
- Immortal Regis
- Shakugan no Shana
- The Ga-Rei manga toss the role of "boy" and "girl" like volleyballs, but eventually it's between Kagura and Yomi.
- Xenogears is probably the Most Triumphant Example of the trope in gaming. Bonus points for having not only the current conflict, but also much of the world's history resting on the shoulders of the lead couple's Reincarnation Romance.
- Blue Drop, a human girl and an alien girl.
- Puella Magi Madoka Magica has magic dependent on Emotional Powers, so by the time of The Movie's conclusion, the powerful relationship between Madoka and Homura ends up being the cause of numerous reality rewrites.
- The second Drakengard game.
- Eureka Seven is a quintessential example, in which the blossoming love between a 14-year-old boy and a blue-haired Human Alien literally saves the entire universe.
- 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 Sailor Moon, the forbidden love between Usagi and Mamoru was the reason their old world collapsed. In their reincarnation, their love becomes the sustaining force that helps her save the present world.
- A Western example is the Bad Wolf arc in Doctor Who. On a smaller scale, the Impossible Girl arc is, too.