Isekai Mahou wa Okureteru! (WN)

「Suddenly Transported to Another World」

"Owww...." – Suimei

Suimei leaked an anguished voice from the pain on his bottom, which was the price for the sudden event to which he couldn't even react.
It came from nowhere. Sure, he had forecast that something was going to happen, but it was too sudden to ready himself.
The floor was hard. Probably a stone pavement or tiles. Falling flat on his backside, his tailbone was in anguish. That was happened just a moment ago.
So, how did it come to this? He didn't even need to recall it, since it only happened a few seconds ago.
On his way back from school with his two friends, he was pulled with his friends into a teleport magic circle that had suddenly appeared on the road.
And at the teleported destination, he had hit his bottom.

(......Man, what a blunder.) – Suimei

Suimei had explored secret magic in the modern era with lot of skycrapers. He only started practicing magic around twelve years ago but he was pretty confident with his skills. Yet, he as a modern magician was easily fell for this trap magic set up by someone else..

He had sensed it and even seen it, yet he couldn't react and simply watched.
If that wasn't a blunder, then what? He felt ashamed and disappointed to himself.
With still teary eyes from the pain on his bottom and the humiliation, Suimei suddenly faced sidewards, worried about his friends who had walked besides him—
"Oww..." – Reiji

Right next to him was his friend Shana Reiji as he also struggled with the same pain on his bottom like Suimei, who was still rubbing his bottom.

"Hey, Reiji. Are you okay?" – Suimei
"Yeah, pretty much. You?" – Reiji
"My ass hurts. Seriously, I feel like it had been split in half..." – Suimei
"Hahaha, you too, huh— Wait, is it just you here, Suimei?" – Reiji

For a moment, Reiji laughed by Suimei silly joke. But then, he who felt uneasy noticed the absence of their other friend Anou Mizuki, who had walked with them.
She certainly wasn't here. The girl, who had walked next to them just a moment ago, was nowhere to be found.
He looked around briefly. The round room was enclosed by stone walls and except the old candle stand, which gave a dim illumination, there was nothing. No, there was something: A solid door and a pattern on the hard floor they sat on, the teleport magic circle.

"Y- Yeah, Mizuki isn't here..." – Suimei

Suimei muttered with somewhat perplexed in anxiety expression over his missing friend. Meanwhile Reiji started racking his brains with an even more bewildered expression.

"Why... And where are we...?" – Reiji

"I don't know either. But I do know that we were brought to this unknown place by someone's will." – Suimei

"...You mean by that?" – Reiji

Reiji looked dubious at the big magic circle on the floor. Suimei followed his suit and looked at it again too. Within one big circle were drawn four more circles and the geometric patterns in it didn't even match the western four or five elements, nor the Chinese five elements. And words he had never seen before on a magic circle were put in place there.
He could tell that the circle was similar to the summoning or séance ones that he developed himself, but that knowledge only applied to him. Reiji, an ordinary guy, obviously didn't know anything about it. Suimei knew him ever since middle school and yet never told him that he was a magician. Therefore Reiji could only know about the thing at his feet from subcultures like manga or anime.
And suspicion started to arose inside Reiji from that. He could only had a vague guess that maybe this thing was the reason for their current situation.