After a short walk, we arrived at the room.

What the hell is that...

　In a large room with a bronze door, a huge snake was coiled around a giant snake.

　A snake with a body as thick as a large tree and black scales.
　However, its upper body was human.
　As black as the scales were, the skin and arms were human. However, the head is back to being a snake again. It was a deformity like a god worshipped by an evil religion.

　The two arms are also holding a huge sword, but the eyes of the snake are closed.
　Is it sleeping...?

That was Naga.

　Amu, who was looking in through the doorway together, said.

''I've never seen it before either. It's probably the boss of this dungeon.
"Boss?
It's the core of the dungeon, or the monster guarding the core.
I see.

　If we defeat that one, then this dungeon will be complete.

Maybe a way out will appear after you beat the boss?
'It can't be a dungeon that goes down to the lower levels. But this place has been flat for a long time, and I have a feeling it's based on the ruins... maybe. There seems to be a passage at the back of the room.
Okay, then....
But I don't think it's a good idea.

　Amu interrupted him.

'Why?'
''Naga is a pretty strong enemy. In a party of six, they all need to be at least fourth level, and in a party of four, they need to be at least third level. Moreover, I've never heard of a black Naga before. Normally they're sand-colored, but a red one spews fire, so that one probably has some kind of special ability. It's too dangerous not to know that.
....
Let's turn around. There's got to be another way in. It's safer to find it.
We can't do that, Amu. We're not prepared to spend much time exploring. We should all be glad we found this room when we have some time left on our hands.
....
Let's take that thing down. Even if there's no way out beyond the room, if we crush the nuke, the monster threat will be gone.
Seika are you sure you can beat that?
Only with Amu.

　Amu suddenly lowered his eyes and gave a small smile.

'All right. But if it doesn't look good, run. Okay?
I'm good at running away. I'll let you know if I need to retreat.

　You know what?
　You can always run away.

　Amu pulls his staff sword from its scabbard.

'On the count of three, we'll go. The naga should happen when we get into the room, so shoot your magic before you get into position.
Yes, sir.

　Let's do it without any signs or warnings.

"Three, two...

　I'll float a crucifix.

"Ow!

　Amu kicked through the door and sprinted out.

　The Naga's snake's eyes opened in a heap.
　He spreads his arms with his sword and turns his attention to the intruder, Amu.

《Wood Phase-----Pile Driving Technique

　A log-like stake of a log, an oval (ashlar) stake, was released, flicking the sword away from the Naga's left hand.

　And the second and third ones hit his chest and torso, making him stagger wide.
　The power is different when done properly, after all.
　It's just.........

...it's shallow.

　It didn't do much damage.
　Naga pulled out the stakes in his chest and belly with his left arm and turned his vertical pupils to me.

"Don't look aside!

　When Amu fired a fireball (fireball) at the snake's head, the Naga staggered as if it had flinched.
　The huge sword wielded with his right arm, Amu bounced it back with his foolishness and tossed it around with more magic.

　Oh?　This one's free.

The wooden phase - the art of staking

　A very thick stake struck the Naga, who was distracted by Amu.
　They stabbed at her shoulder mouth and throat one after another. It seems that a good deal of damage has been done this time.

　I see. Is this the role of the vanguard?
　Thanks to Amu's constant attention, it is easy to use jutsu even during battle.
　Even in the past life, if a warrior and a sorcerer cooperated, it would have been easier to exterminate demons.......

''Be careful!　Something is coming!

　When I looked, I saw that Naga had inflated her rib cage.

　It thrusts out its upper body and spews liquid from the mouth of the snake.

　The floor with the liquid on it was bubbling and dissolving.

　You're spitting out strong acid?
　Heh.....

　It is also a good idea to make sure that you have a good idea of what you're doing. But the stake of an ashtray flicked off the stake.
　It's a good idea to make sure that you have a good idea of what you're looking for.

It's a very good idea to have a good time. Can you take on the attack?
Okay, okay!
And when I tell you, fall back.

　While supporting the vanguard Amu with 《Pile Driving》, I look for an opportunity.
　Not yet, not yet........

　Eventually, when the Naga was turned upside down by Amu's magic, its rib cage swelled up.
　A forward swing of strong acid.
　Here.

''The golden phase - the art of the explosive nail

　A white metal spear protruded into the oral cavity of the snake, which had nearly spat out strong acid.
　The strong acid that leaked out of his mouth melted the spear and his upper body, and Naga writhed with a silent scream.

''Alright, back up!''

　He gave a signal to Amu and tried to shoot the 《Oni Fire》.
　But it was blocked by the rampaging tail.
　No, it's completely alerted........

　Wait, you don't have to do it yourself.

Amu!　Shoot a fireball at his head!

　I call out that to Amu, who was in an easy position to aim.
　Instead of a reply, a fireball spell was fired.
　It flies precisely to Naga's head and...

　A flashy blast of fire went up around the spear.

　There was no longer any defense, and the half-human, half-snake monster was flailing about on the ground in a mess.

''You've finally put your head down.''

　And in the eye sockets of the still burning snake head----Amu's staff sword was thrust deep into the eye sockets of the snake head.

　The human's upper body and the snake's lower body convulsed violently.

　But eventually........the dungeon boss Naga stopped all of his movements.

　The flow of power suddenly weakens and disappears.
　It looks like she's dead.

　Huh, it ended easier than I expected.

'Amu!　We did it...
Seika!

　Amu runs up to me and hugs me as it is.

'Yay yay!　Ha-haha, I've never taken down a dungeon boss before!　I mean, we just threw a party, and now we're in perfect harmony.

　Amu was jumping up and down, taking my hand in hers.
　I'm not going to be able to say that I'm not going to be able to do anything about it. I'm sure he's not an irrational reincarnation like me, but it's probably just a coincidence.
　I'm not sure if she noticed my bitter smile as if she were looking at a young child, but Amu shyly removed her hand and cleared her throat.

"But you're also reckless. You don't need to go out and punish a guy who is running around with fire.
'Some of them replay it when I lean back and stuff. It's a good thing I got it right.
'Yeah, that's great, Amu. That's not something you can do very often.

　There were warriors in Japan who slayed demons in human flesh, as if they were demons themselves, and the way they fought reminded me of that.

　As I was stroking my red hair while thinking about what to do, Amu turned his eyes to me.

'What, this hand?'
Oh, I'm sorry.

　I let go of Amu's head in a hurry.
　I do this to Yifa sometimes, but it makes me feel like I'm dealing with an apprentice.
　It's like I'm treating him like a child and he won't like it, so let's not do it.

　Amu turns away.

''Well it's fine, but...''
What?
It's nothing. More importantly........what is that silver spear?　It was a fire magic explosion.
It's just, well, that's just the nature of the metal.

　A metal discovered by an alchemist in the ancient Greek city of Magnesia, Magnesian silver (magnesium), has an unusual property: it burns on its own.
　Moreover, it dissolves easily in acid to produce flammable gas, so such an explosion could easily be caused by using the explosive nail.

　I was just vomiting strong acid, you know.

Are you hurt?
"...no. It's unnatural. I thought I had some minor burns.
'Then the spell I gave you must have taken the place of the spell I gave you. I'm sure they'll still keep it at all.
'Can you do that?　That's useful, isn't it?
That won't heal a serious injury, though. Now, let's move on.

　As I walk out, I look up at the ceiling and say, "If there's a way out, we'll be right by the temple.

If there's a way out at this point, it will lead us right to the temple.
"...?　How do you know that?
Oh, no. Somehow...

　Amu looks at me quizzically, and I rush to disguise myself.

　Yuki asks me in a whisper, "Seika-sama, do you know where you are?

"Seika-sama, do you think.......do you know where you are now?
Well. It's been a while.
How did you...
You have to use your magic to make the magnet work.

　A magnet's ability to attract iron - magnetic force is one of the few forces that can influence the thick earth's crust without being dampened.
　If you generate a powerful magnetic field with sunshine, it can reach the earth's surface even if there is some distance between you and it.
　This was detected by the shikigami who had been transformed into bees.
　There are minerals in the abdomen of the bees that react to magnetism and can sense changes in the magnetic field. Of course there is no such thing in the formula, but it works according to the specimen, so the function is the same.
　By varying the position and height of the magnetic field, and capturing it from the ground, they were able to get a rough idea of their current location.

　Foxes and pigeons could have done the same thing, but when it came to detecting small changes near the ground, bees were the best.
　It was hard to see, though.

'So, by any chance, could you have escaped at any time using the swapping method?
Yes.
Why did you go to all this trouble to...
I just told you.　I just wanted to have fun. I've never been to a dungeon before.

　Also, I wanted Amu to gain experience.

　---- To have him become the strongest eventually.