Shikkaku Mon no Saikyou Kenja~ Sekai Saikyou no Kenja ga Sarani Tsuyoku Naru Tameni Tenseishimashita~

"…Keeping silent won't help you. Even if you're invisible with naked eyes, you're plain as day with that much mana emitting."

"…Mathias, could it be that there's a demon inside this castle?"

The king sounded surprised when he heard me.

"No, it's not the main body. It's a spell art unleashed by the demon."

"Spell art… Is that some kind of wiretapping?"

"Something like that. You cannot see it, however--"

I took out a wood chip as I said that and threw it at the corner of the room.

The chip drew a parabola and got repelled as if it hit something one meter before the wall.

"Looks like it has a substance. Though, the demon won't suffer any damage even if that's physically destroyed."

Judging from the spell art, it's most likely a variant of magic called 【Fixed-type Simple Mana Interference】.

It's a relatively simple spell art which can be used to monitor far-away places.

In addition to that, it can also be used to turn up documents and send voices.

Furthermore, it doesn't have enough power to kill but conversely, the user also won't receive any damage even if the spell art is attacked.

In a way, it's a magic with an extremely good cost/performance.

"I can't believe it…"

The other three beside me seem to be shocked.

And the demon ('s magic) doesn't look like it'll make a move either.

Well, that's probably the correct answer for the demon. You can't really tell it apart from simple barrier magic as long as it doesn't let out a sound.

--That's why I'll make it speak.

This spell art has two weaknesses in exchange for its low mana consumption.

First, it needs time to set up, and the range is quite narrow.

It's not very effective unless it's set in a room where extremely important conversations are carried off.

As for the other weakness, I use up all my remaining mana and construct a very small-scale magic.

"Guh, what the heck is this…"

Right after that, a perplexed voice resounded from the corner of the room.

You cannot damage the user of 【Fixed-type Simple Mana Interference】 through the spell art.

However, that only applies to physical damage and simple destruction through magic.

The information gotten from 【Fixed-type Simple Mana Interference】 is processed in the spell art user's brain.

In other words, if you forcefully send harmful info for a demon mixed in the actual info, it's possible to directly destroy the brain.

"GU, GUAAAAAAAAAAA!" 𝗳𝐫𝘦e𝘸𝗲𝚋𝓃𝚘v𝘦𝘭.𝑐𝒐m

The spell art broke along with anguished voice, and the space in the corner of the room warped. Apparently the spell art didn't have emergency cut-off function incorporated, however the magic itself is disintegrating as the demon loses control over its own mana.

I supported the spell art for half a second using my remaining mana before I ran out of it.

The spell art that lost its support disappeared with a clank sound.

"…Did you kill it?"

"No. It'll leave an aftereffect somewhat, but the demon probably hasn't died."

Even if I have my usual amount of mana, it probably won't still be enough to kill the demon.

The user would have been killed if it was a human, but a demon's brain is sturdier than that of a human.

"…I see. My gratitude for your help. To think they even slipped into this room…"

"About that matter, Your Majesty. Did the voice earlier sound familiar to you?"

"Now that you mention it, that voice was… of the previous Magic Division Commander, Elhart!"

Thought so.

"Did Elhart ever come into this room?"

"Many times. He got us during those times huh…"

Then we can safely assume that the culprit is Elhart.

He probably could set up as many similar spell art as he wanted since he was against humans who couldn't even use 【Passive Detection】.

"For the time being, I will set up barrier that can intercept wiretapping magic on important rooms like this one."

"You could do such a thing?"

"Some magic can't be intercepted, but it's better than nothing."

That said, such magic are all complex magic, the present demons highly likely can't use them.

If I just put a warning system for when the barrier is destroyed on it, I'm confident I can deal with it.

Ruli will be the one who does the augmenting though.

"By the way, 348 kilo to the west from here, and then 4425 kilo to the north. Do Your Majesty know what's located there?"

"…Hold on."

The king took out a map from a drawer.

"It's still inside our kingdom, but there is only a remnant of an abandoned village destroyed by demons in the past around that area. …Don't tell me, Mathias…"

"Yes. Looks like we've found the demon's location."

Using such a poor monitoring magic in front of me would only result in getting traced back instead.

Now then. It's a bit far, wonder how should we go around to attack them.