"Having monsters coming out in a place where it's easy to fight above ground is the best possible chance to gain experience points. It's no bad news at all."

  "T-treating monsters like mere resources…"

  "They are resources though. Moreover, if we know where they will appear, we can prepare a trap. There's never been a better situation. …and so let's go have a look at the Dragon's Vein while we're activating the barrier."

  "Dragon's Vein?"

  "Yeah. As Dragon's Vein is an enormous lump of mana. You can look at the Dragon's Vein if you need to observe magic, convenient stuff."

  I know that the summoning magic has gone haywire, but observing from the surface only nets me a rough picture of the way the monsters will appear with my current detection capability.

  We've got to go there to activate the barrier anyway, so might as well.

  "I saw the Dragon's Vein when I installed the magic stone… But it only looked like a jumbled mix of mana inside the soil to me…"

  "Me too, it doesn't feel like I can get anything from watching that stuff…"

  Well, it's probably still a bit too hard for Ruli and Alma.

  Dragon's Vein does look like a jumbled mess after all.

  Once you get used to it, you can read things like its composition and such.

  "It's alright! I don't understand either!"

  "…Eh? Iris, you should know about it shouldn't you?"

  Just as the name suggests, Dragon's Vein are used by dragons for stuff.

  Like say, instead of using maps, they make use of Dragon's Vein, there's no way she doesn't know——

  "I can understand its rough geography, but even dragons don't know how to distinguish a slight magic mixed in the vast Dragon's Vein! The only one who could do that is Mathias-san and… no, only Mathias-san!"

  She was going to say more just now.

  Was she trying to hide something perhaps.

  "Weren't you going to say someone else's name besides me there?"

  "There was another person, but not anymore."

  Iris replied to me.

  So there was someone who could do it in the past.

  Now that I think about it, I never met anyone who knew how in my past life, but I'm sure those people did exist and only didn't want to say it out loud.

  It's not a particularly hard technique.

  It can't be helped now since magic technology has declined, but there must have been a lot who could before the decline.

  "By the way, that person said 『I'm going to reincarnate. Please don't look for me』 as his last before he passed away."

  Such a guy——hm?

  Isn't that the past me!

  "And the one Iris knew was only that person?"

  "Only Mathias-san and that person."

  "…Well, Iris is a dragon. It's should come as no surprise that she doesn't know much human techniques."

  "I think Mathias-san is worse here in the sense of not knowing the technique level of normal humans…"

  We arrived at the Dragon's Vein while having that conversation.

  The magic tool has been installed inside the dug Dragon'S Vein just like how I asked them before subduing the demons, and one part of the magic absorption installation is already in operation.

  With this we can start the barrier anytime once the other devices are in places.

  I checked the Dragon's Vein before starting it up——the situation has gotten quite interesting.

  The magic that had been there fused together with mana of the dead demons, turning it into quite an extraordinary situation.

  Looks like I can expect much, in many ways, from this.

  And also, judging from the Dragon's Vein state, the monsters will be summoned tomorrow noon.

  Even the amount of mana I will have to use to activate the barrier won't be recovered by then——

  Which means, let's start the barrier for now.

  It'd be troublesome if some demons were to infiltrate during this time.

  "I'll go make the space to insert the barrier, wait a bit."

  "Yes!"

  "Got it!"

  "I understand!"

  After hearing the three, I start to dig the surrounding walls.

  I could do it freely now since the parts needed for the Dragon's Vein were finished already.

  Afterward, I put together the barrier composition with the help of the three.

  Lastly, the main event is augmenting the magic device.

  "Ruli, carve this magic circle into this magic stone."

  I took out a magic stone and a paper drawn with a magic circle.

  The subjugation back then was over by the time I arrived, but I knew that Ruli had succeeded augmenting the magic circle I gave her back then by looking at the dead prickled demon in the schoolyard.

  This one is simple compared to that.

  "Yes!"

  Ruli quickly finished augmenting the magic device after saying that.

  Her skill really has improved remarkably.

  The Ruli before the fight against the demon couldn't have possibly augment that magic circle.

  Yet, counting on her getting it right after repeating for many times, I still gave her the magic circle.

  The weights of experience between augmenting in the heat of battle and peacefully augmenting with no penalty in failing greatly differ.

  "Well then, here it goes!"

  I started up the completed magic device as I said that.

  The magic device vibrated with a dull sound and then it stopped before long.

  The mana supply from the mana collecting device has stabilized.

  Looks like the barrier has been activated safely.