We resumed our steps, and it was about an hour (*thirty minutes).
　The sewer was approaching the point of a gentle curve.

'Seika.'

　Mabel is approached from behind.

'How far are we from where the ring is?'
'Hmm, it should be about time...'

　And I stopped.

"Amu, wait.
What?
Another flock.

　Amu looks at the end of the passage with his eyes.

'....Where?
You can't see it from here. There's a roomy area just around the corner. There seems to be a lot of them in there.
How could you possibly know that?
Sort of.

　A small bat returns from the end of the aisle.
　When the bat returned to its starfish state, it became invisible and melted into the landscape.

　Even in complete darkness, the bats' vision works.
　Those things are inaudible to humans, because they see their surroundings in a high-pitched tone.

'It looks like they haven't come out into the corridor. I think we can get a little closer.

　I took over the lead and proceeded cautiously.
　After a while, I see a place that looks like a room.

　The walls of the corridor seem to disappear and there is a space where the materials are stored.
　I'm sure it was used as a space to store materials during construction.
　However, the entrance to the room was spread wide open, as if it had been battered by something.
　The interior of the room must have been quite large.

　Otherwise, there's no way we would have felt such a frightening presence.

　Even though we are still far from the room, there are countless small signs of life, such as faint vibrations on the ground and the sound of something being gnawed on, which can be clearly sensed even from here.

　I wonder if the girls behind me could tell, too, that there was a tense atmosphere in the air.

　I couldn't help but sigh.
　What a bother.

Want me to do it?

　Yifa says enthusiastically, but I shake my head.

No, I'll do it this time.

　If there's a leak, we're in trouble.
　Let's make sure we get through this.

　I approach the room's entrance cautiously.
　Then, I quietly formed a sign.

''Phase of the Earth - the Art of Penetrating (Tootori De).

　Several pillars of quartz erupted, blocking the entrance to the room like a cage.
　Ferric rats rushed in when they noticed the change, but of course they couldn't get out.

　That's good.
　I set up a ward around Amu and the others, and then sent a single Hitogata flying and slipped it between the pillars and into the room.

　Now, will this kill me?

The art of the poisonous phosphorus mist, a phase of earth, metal and water.

　With a swooshing sound, steam spurted out of the heater with great force.

　Then the rats inside began to rampage as if they had gone mad.
　With a high-pitched scream of demise, one by one they turned over and convulsed.

　Before long, the sewers were quiet.
　After a short period of time, I sent the human remains of the curse flying to eliminate the miasma from the pillar of the "Tootori de" and the miasma from the "poisonous phosphorus fog.

It's not just a matter of time before the miasma disappears.

　I reply to a puzzled Amu.

"You let him breathe the poisonous air.

　When phosphorus (phosphorus) reacts with a strong base (alkali) of water, a colorless, fishy, poisonous gas is produced.
　It's enough to kill a beast of that size without inhaling a large amount.

''Poisonous air... like the kind you get in the mines?
'You know it well. It's not the same thing as that one, though.

　As I say this, I step inside to check out the room.

　The lights of the human gadgets illuminated the carcasses of ferric rats. There were a tremendous number of them. This must have been a nest of sorts.

　I let the Hitogata fly further back.

　And then.
　The light was suddenly swallowed by something that appeared out of the darkness.

　What floated in the light for a moment was a dull, glowing fang and snout.
　It didn't let the Hitogata fly again, but immediately pulled Amu and Yifa, who were nearby, to the wall.

　The next moment, a black shadow rushes in from the darkness.
　The shadow passes through the space we were in a moment ago, ripping away the space. It runs out of the room, splashes across the waterway, and crashes into the opposite wall.
　The impact causes dust to fall from the ceiling.

'Wha, what, that!'

　Mabel, who was standing outside the room watching the passage, yells out in surprise.

　I let the lights fly and observed the shadow of a new monster.
　It looked like a tall, rat-like creature.
　The long, slender tail, squat limbs, and rounded ears are typical.
　However, its body length reached two and a half feet (*seven and a half meters). It was a huge size.
　Furthermore, its body had no fur, but was instead covered in a layer of metal leather that looked like sheet metal glued together. It looks hard to the eye.

　I tilt my head in the air.

"Um, what was it called?
'Oh, it's an adamantine rat!　I never thought I'd be out in a place like this!

　Amu shouts in astonishment.
　That was it, that was it. He's like the master of the ferric rats.

　Hmm, if he was there, he should have breathed in the miasma from the 《poisonous phosphorus fog》, but....but since it was that big, it was simply not enough. That poisonous air is lighter than air, so if you lay your head down and stay still, you may not be able to make them breathe a lethal amount of the miasma.

　The adamantine rat pulls its head out of the wall and slowly turns around to face us.
　His glazed eyes are surprisingly cute, but he is clearly furious with us, the intruders.

Yifa, don't move from the wall.
What?

　I stepped out into the center of the room and pulled the lighted Hitogata over to me and flashed it lightly.
　The black eyes of a giant rat turned to me.

　It began to charge again.

"Mm.
Oh, my God!

　As Mabel and Amu passed each other, they slammed their battle axes and staff swords into each other.
　However, they were played vainly with a hard metallic sound.
　It's a good thing that you're still very hard.

''Seika!''

　I was in the direction of the rush, and Amu turns around and shouts to me.
　The huge metal body is just about to send me flying. I switch positions with the ceremony at the wall.
　The rushing giant rat blows the replaced Hitogata away with the wind pressure, and its momentum carries it into the wall at the back of the room.

''Ha, it's more of a boar than a rat,''

　I'm sure she can't make small moves with her body, and that's a reasonable way to attack.

　And then I turn to the girl with the axe and say, "You know, Mabel.

I'm not going to be the only one. It's not just Amu, but you too?
...and your weapon is too light.

　Mabel said frustratedly.

　The battle axe I have now is big enough, but it's much smaller than that one I had in the semi-finals.
　I don't think I could swing that thing in the sewer, so I can't blame her.

　Adamantolat flinches.
　The two girls in the vanguard rushed in and leapt in front of me.

'Seika, stand back.'
Oh, you're the rear guard!　Why are you provoking me with your light?
Yeah, but...

　Their main attack is a rush, and their vanguard is usually overtaken, so I don't think there's much point in forming a formation anymore.
　And if I didn't pay attention and let Yifa get to me, it would be a problem.

　I'm sure they are trying to fulfill their duties as the vanguard.
　Maybe we should let them hold the flowers.

　I fly a few Hitogatas.
　They stick to the metal hides of the giant rat that was about to turn around.

　I make a sign.

The golden phase - the technique of calomeluric chloride.

　The silvery liquid seeping from the human gadget slowly invaded the metal leather.
　The Adamant Rat, who had been lowering his body for the rush, suddenly opened his eyes.

''Eggy------!

　A giant rat was rolling around the floor of the room in a mess.
　It seemed to be trying to peel off the stuck human gadget.

　Unexpected. Does that metal skin have any senses?

　Eventually, the human gadget, torn by friction, lost its strength and fell to the floor.
　An angry giant rat glared at me, baring its teeth.

''Oh, he's ready to cut,''
What?

　Three thrusts begin.
　Amu readied his sword and shouted as if he were burned out.

''Oh my god, I'll do it!

　After fluttering and dodging the rush, Amu's staff sword was swung at the giant rat's right forelimb.
　A flash that was played earlier.
　But this time - the mithril blade shattered the metal leather like candy cane and cut off its leg.

''Nggggggggg!

　We lose the leg that was supposed to kick the ground, and the adamantine rat rolls to the floor in a pinching motion.
　I'm sure you'll be able to find a way to make it work.
　I'm sure you'll be pleased to know that I'm not the only one.

　There is a roar as if a boulder had fallen, and the entire sewer system shakes.

　Adamant Rat's head was completely blasted open and cracked.
　Pulling the battle axe out of the sludge of blood, brain plasma and metal fragments, Mabel, covered in return blood, carried it on her shoulder.

''Hmph.''

　He let out a satisfied snort and then tilted his head.

'It was getting soft, I think,'

　And then she looks back at me and asks, "Did Seika do this?

"Did Seika do this?
Yeah, I do.
'How?　I thought I saw something that looked like silvery water, though.
'Well there's a metal like mercury that makes other metals brittle,'

　The Mercury of Gaul (Gallium), a metal discovered by an alchemist in the Frankish Kingdom, had the property of tearing it to shreds when it came into contact with another metal.
　It was possible to make it that brittle even in a short period of time if it was efficiently eroded using the technique.

''I've heard a similar line before.

　Amu, who had come nearby, said in a dumbfounded manner.
　Then, he suddenly looked embarrassed and began to speak in a rambling manner.

''Also, I'm sorry for...''
Hmm?
"Well to be honest, I guess I didn't see it coming. The Iron Rat Pack and the Adamant Rats wouldn't have been able to make it without you and Yifa.
Don't worry about it. It's the job of the rearguard to burn it down with magical firepower.
'Nope. Normally, the vanguard is supposed to be the wall, drawing attention to the situation. If you weren't the vanguard, this party could have fallen apart... I knew I shouldn't have said anything so easily about diving into the sewers. I got a little carried away. I'm sorry.

　Amu slumped his shoulders in a daze, I thought for a moment, then smiled and said.

'Hmmm, yes. But it's enough if you're able to reflect on yourself. You're alive now, no matter what. You can use this failure to help you next time.
'Yeah...'
I also broke my own formation. In hindsight, it would have been better to have Amu and Mabel draw attention to it and not let them rush in.
Hmm....
'Amu is the one who knows the most about adventurer affairs and monster slaying. Remember my promise, don't you?　I'll be counting on you the next time we go on a more proper adventure.
"!　........yes.

　The usual.

　I laugh and add, "I'll tell you what.

I'll tell you what," he said, "you should be more careful about what you pick up in the kitchen. Violet and Huyumaru said that you should be sorry for picking up food in the kitchen. You don't have to be so...

　I reached for Amu's head as I said it, and then I realized and pulled my hand back.
　I was just about to do it....

　Amu, who has been tilting his head, turns away when he sees me pull my hand back.

"....why do you try and stop?
What?
It's nothing!

　Amu says angrily.

'I mean, what's a pinch of food?　I didn't do that!
'Eh....'

　I was speechless, my eyes widening.

Did I... did I say that?
I told you!　And what did you say?　Sumire?　What region of the country are your students from?　Is there anyone like that?
No it's nothing.

　I held my hand over my mouth and looked away from Amu, who was looking at me quizzically.

　.........It's crazy as expected.
　I'm going to be able to say that I'm not going to be able to get my memories of my previous life confused with those of a time long before I was reincarnated.
　Is this the evil of having lived too long?

　----It's not a good idea.

　No..........no.
　It's just that Amu's behavior just now overlapped with that girl's, and I had a strange feeling.
　That's right, that girl was also like that, getting carried away and failing like that, she was depressed by herself.

　Could it be that he had an unfinished business?
　For not being able to watch over that kid to the end, just like the disciples before him.

''Seika-kun!　Over here!

　I huffed at the voice and turned around.
　When I looked, I saw Yifa, clad in the faint white light of the Spirit of Light, beckoning to me at the back of the room.

''........What's up?''

　As if to fool something, I trudged toward it.

　As I scattered the human remains of the lights as I walked, I realized that the room was much larger than I had expected.
　Apparently, the rats had bitten off the walls of the original room and spread it out considerably.

　At the far end of the room that Yifa was pointing to, a little farther back in the room.......there was a large pile of junk of some sort.
　Most of the junk looked like scrap metal, whether it was chains or nails or a piece of armor.

''Ferrikrat collected it, right?　But why...
Oh, I think it's bait.

　Amu, who was following behind me, said.

'Iron rats and adamant rats eat metal too, but they don't seem to need that much. So they store what they don't eat at once in their nests like this.
Well.....

　They look like ants.
　Speaking of which, I had heard that further south in Egypt there are hairless rats that dig nests in the ground and live in groups like ants.
　Maybe that's why there's a huge population of felic rats, because the parent adamantine rat wandered in from somewhere and was able to create a community with that one at the top.

'Seika.'

　And Mabel, from behind, pokes me around my waist.

"The ring. Maybe it's in there.
...Ah!

　I forgot all about it.

　Then we all started to turn over the pile of junk.
　Only thing I've realized since we started is that it's a little overwhelming.
　We're going to find this...?
　As I moved the sheet metal away, a small silver ring reflected the light.

'Oh!'

　I pick up that little ring.
　I find it.
　Come to think of it, I haven't asked you for details about the shape of it, but I'm sure it's the one.
　I pick up the ring and shout, "I found it!

"Here it is!
I found it!
Here it is!
I think it's...

　I look around and see that they all have rings in their hands, just like that.
　I say in frustration, "No, no, which one?

"No, no, which one?

　This might be the only way to contact the guild once and have all the junk moved out.