Yuuto

in the lore of this world, it's set slightly in the future, but far enough that science can now be somewhat used to interact (in a limited capacity) with alternate universes (but its still kind of iffy)

of course humans wouldn't be able to reach alt. universes that "far away" at all due to such limited technology, so usually the results/products of these experiments are negligible

however, 25 years ago, in a particular alternate universe (extremely far away) which contained a society based around the use of special high-tech swords and was governed by a "god of darkness" + "god of light" , a sudden spacetime rift appeared, which not only rent that universe asunder, but separated the two gods from each other. each of them were supposed to carry their respective swords of "darkness" and "light", but at the time, the god of darkness was carrying both of their swords, and so he was not only separated from the god of light, but he also had no information to go on regarding trying to reunite with him, because the light god had lost possession of his sword

the god of darkness had no idea where the god of light ended up, but as for himself, he ended up in a rift between universes that was EXTREMELY close to the universe that the scientists resided in (the version of Earth where the main story takes place.) 

This allowed scientists to get in contact with this "unknown entity"

The scientists pressed the god for it's ability to create "ether" swords/ the secret to create them, and gave him a tempting offer: Collecting the data from the usage and statistics of the swords might help the scientists pinpoint the light god's coordinates, or at least the universe they came from. Agreeing under these terms, the dark god shed his original form (which was more like something similar to a large black dragon) and took a human form. He then stored his original form (which was now simply an empty "vessel") in a pocket of space.

the information that there was a "god" in existence, another god (the god of light) and that the swords came from another universe was kept extremely confidential. 

And so, the mighty god of darkness ended up working a "regular" job at a shady(?), "run-down" ether sword shop nearby the World Arena. (the world arena is the largest arena globally for "Ether Battle"! respectively, the area around there is very "trendy" and high-end!)

"Ether Battle" is the sport that was made with the technology the dark god brought from his universe-- Ether Swords! With science, they were modified to react with certain "barriers" that allow them to be used safely without "actually" hurting opponents, and then created rules to develop it into a sport! Within the span of 20 years, Ether Battle took the world by storm. It's the most played sport worldwide!

However, in order to Ether Battle, you need an Ether Sword. But you'll only be able to use an Ether Sword if you "resonate" with it. that means you have to pick up the sword to test if you are "compatible" -- if you release an "ether output" and the sword slightly changes shape, you passed! But if it releases nothing and does not turn off, you'll be unable to use that specific sword. Generally speaking, people can easily be compatible with countless possible swords. But in some cases, you might be compatible with almost none... or.....?

back to the god of darkness.... He's running a shop in order to collect data on the usage of ether swords he distributes. 

He's a little eccentric; somewhat aloof, and often seems tired or disinterested in running the shop (or maybe he doesn't prefer doing such boring work?? well at least thats how he puts it) so when later on, a data analyst from the government comes to assist him with collecting Ether Blade data usage, the god of darkness just assigns the data analyst the role of running the shop, and the god just does the data analysis himself!! (to the assistants dismay) Although, the god of darkness just sleeps nearly all day, and then wakes up for a few hours during the night to get his work done (lazy? careless? the assistant is really exasperated with his boss....)

anways, about the swords being sold in the shop..... the Sword of Light, collecting dust, lies in the discount section. The gimmick is: if you can successfully resonate with it, you can get it for free. otherwise, you can't get it at all! the logic behind this is simple: the only one compatible with that sword is the god of light, who the god of darkness got separated from. so this is the perfect "trial" for trying to find his companion.

...But, no one has been able to activate it thus far and counting, so it just sits there collecting dust....

Until one day the bell on top of the shop door rings and the napping god instinctively wakes up...!

The young man who came in, Yuuto, a college student who just moved into the city, is looking for a sword that isn't too expensive... because he used up nearly all his money just to move to the area and attend college there!

The assistant (who just appears to be the stores manager) leads Yuuto to the discount deal section, but Yuuto is immediately drawn to the dusty Sword of Light...

The assistant tries to tell Yuuto "not to bother" because that sword has been "broken for ages" (no one can activate it) but the god of darkness comes out of his office behind the counter just then (which he usually never does during the day) and insists to let Yuuto try the sword

yuuto is able to activate it with an overwhelming output of power that leaves him passed out for three days... but despite that , he gets the sword for free as promised! but...

The god of dark is convinced that Yuuto must be the god of light in some way. (reincarnation is the most likely reason, he figures.) He asks Yuuto to work at the store, and in return, offers to sponsor him officially for the upcoming World Championship in Ether battling! (paying for all of his expenses.) Yuuto readily agrees, and begins working there and entering the world of Ether Battles, rising to the championship all the way from the bottom.

But something dangerous is brewing outside the walls of the stadium.... 

"Cursed" Ether swords that can be used outside of a barrier.... and can actually kill...?! ...

A rumor spreading around that fighting with cursed swords to kill 100 other wielders and steal their swords will grant a person the powers of the "God of Darkness" ... but the actual god of darkness knows that someone must be trying to impersonate him ... And the key to unraveling and putting an end to this dark scheme lies in the abilities of Yuuto's sword!