Prolouge

[Demon Lord's Castle, Demonic Empire Barbados]

"Demon Lord Ashborne, what do you plan on doing?" asked the Demon General Yulishia, his loyal retainer.

Demon Lord Ashborne. He was inflicted with a deadly curse, and will be dying anytime soon. However, if he falls, the fate of the Demonic Empire will be unknown. The humans won't hesitate, they will simply eradicate every demon without batting an eye.

He can't let that happen.

"I will die sometime soon. But before that, I will choose a successor." replied the bedridden Ashborne, while coughing.
"Successor?" asked Yulishia, "But no Demon or Human in this world can handle your power, and combined with [Successor's Blessing], there's no way a soul can handle it..."

The Demon Lord Ashborne is the strongest Demon Lord in all of history. His power is on par with the Gods. His soul is unique, and not everyone can handle this tremendous power.
On top of it, his successor will receive the [Successor's Blessing]. It is a gift by the Demon God Astarte to the first Demon Lord. It increases the successor's prowess exponentially. Combined with his initial out-of-charts powers, there's no way anyone can even think of handling it...
Unless...

"I am thinking of summoning someone from another world." Ashborne explained.
"Summoning?" Yulishia was concerned, "But my lord, isn't that what the humans do, to create Heroes? Is it a good idea?"

"Yes. Summoning essentially reflects the summoner's will, and selects the best candidate. That is, it will always choose the destined one." Ashborne explained everything elegantly.
Yulishia was still a bit concerned, but she accepted it.

"Upon my death, they will be summoned from another world. My essence and soul will be merged with them, and they will inherit my memories and all my powers, in addition to the Blessing." said Ashborne, still looking pale, "I hope you will guide them forward, Yulishia."

"As you wish, my lord. Your wish is my command." Yulishia, being the loyal retainer as always, accepted it.

[Royal Palace, Kingdom of Erlsia]

"What did you say!?" King Eugnes von Erlsia exclaimed.
"It is as I said, my lord. The prophecy says that the current Demon Lord will perish within the next week. However, a new Demon Lord will appear, who will be the strongest in all of history, strongest than the current one, with power rivaling even the Gods." explained Pope Charles Ernstein.

"What do you suggest we do, then? Surely you will have a solution to this problem, would you not?"
"That is a given, my lord. And the solution isーsummoning heroes from another world!"

"Summoning heroes you say? But is it wise? Wouldn't it be hard to restrain them? Useful they might be as tools, they are quite hard to control."
"That is of no concern, my lord." replied the cunning Pope, "I have arranged of enslavement magic to be installed to the magic circle. So, they will be restrained from the beginning. They will simply be Your Majesty's tools. After defeating the Demonic Empire and taking over it, we can even use them in wars against other nations!"

"Hahaha, as expected of the Pope of the Holy Church. You are as shrewd as ever. Very well, proceed with it."
"I am unworthy of your praise, my lord. The preparations would take about a week, and then we will be able to summon them, my lord."

[a certain otaku convention, Earth]

"Hey Haru, what are you doing here?"
"Aika!? You startled me."
"So, what are you doing here, Haru-kun?"
"Yuki too? I didn't expect to run into you guys here."

The two girls are Aika Tachibana, and Yuki Shirogane. And the boy they're talking to is Haruki Kurobane, a loner otaku and super-lazy guy. They are childhood friends and classmates.

As it happens to be, they ran into each other in an otaku convention. Well, Haruki being there does make sense... but he didn't understand why these two are there.

Well, it's not like they can tell him that they're secretly otaku too, though. So, they will obviously avoid asking questions now as well.

"So, Haru do you come here every year?"
"Yeah, I do. I don't have friends, so I simply come here to enjoy the food and shows. I rarely talk to anyone in here though."

That's who Haruki is. A total lazy otaku. He's a sleepyhead, who mostly thinks about sleeping. Sometimes about food. And rarely about anything else.

"!? Huh, what's happening!?"
"Haru! You're glowing!"
"Haru-kun!"

Haruki suddenly started to glow. So, these two wrapped around him.
All of a sudden, something happened... and when they opened their eyes... they were in a strange place.

[A certain high-school, Earth]

"About this question, who can answer this?"
"Me, sensei!"
"Oh Souta-kun! Go ahead!"

That guy is Souta Takahashi, the "Prince Charming" of the school, and the top of the class in grades. He's also a lot athletic and allーtotally the "protagonist" material.

Yet, he does everything for a certain reason. To win a certain someone's heart.
"Hey Souta, when are you gonna confess to Yuki-san?"
Yes that's right. The girl he loves is none other than Yuki.

"I will, eventually. I first want us to be friends, though. But I can't bring myself to ask her to be friends."
"Just don't be too late. I heard she hangs out with that Haruki guy quite a lot. I wouldn't be surprised if you were too late and they started dating."
That guy is Kei Tachibana, Aika's younger twin brother.

He kind of has a grudge against Haruki, because he's close with both Yuki and his older sister Aika, and he hates him for that. Which is why he tries his best to persuade the "Prince Charming" Souta to take a step forward and take Yuki away from him. Not that Souta has the courage to do anything, though.

"Ah Kei, stop it. Don't try to scare the poor Souta!" exclaimed Nagamo Yuuto, Souta's best friend, and a pretty level-headed guy.
"But it's true Souta, you do need to have more confidence in yourself. Don't belittle yourself, and have faith in yourself. Don't worry about anything, and say her everything directly."

"You are right. I should probably do it." said Souta, mustering up the courage.
"Very well, tomorrow, I will tell her how I feel!"

Although... little did they know, that the so-called "tomorrow" will never come. Never will they ever see each other and Souta be able to convey his feelings.

Little did they know... the fate of two worlds will intersect, and proceed with an odd development.