Chapter 354.1. Decisive Battle With The Demon God

The Demon God Ashtaroth unleashed the magic dormant within itself all at once. The obsidian chamber, constructed with crackling black energy, vibrated, and stone fragments fell from the ceiling.
“An incomprehensible existence. Perish by the power of this Ashtaroth!”
Releasing a fierce voice that echoed from the frozen hell of souls, Ashtaroth readied its four arms and attacked Miu.
“You don’t understand? You lack discernment! Mii-chan is so adorable.”
Stepping lightly onto the floor with a tap and a side step, the moment I did, the place where I had been standing exploded. 
It was an attack by Ashtaroth at a speed like a gust of wind. One of its arms, thicker than Miu’s torso, pierced the floor, scattering obsidian shards as it withdrew.
“Calling those who claim to be the Old God incomprehensible, what’s wrong with that? I won’t let my guard down!”
[Four Elemental Demon God Arms]
Peeling back teeth like a mammoth, the Demon God began to gather magical power in its arms.
The four arms began to transform under the influence of magic.
One became an arm of blazing flames like magma.
One turned into a transparent water arm-like glass.
One transformed into a light green arm, swirling into a tornado of wind.
One emitted dazzling light, becoming an arm of super-high-temperature lightning.
Each arm had transformed into a mass of elements.
“It’s not just Enchanted magic; you’ve changed the arms themselves into elements?”
“That’s right! And these arms are true elements. Their power is—”
“If they have the piercing ability, resistance and absorption of attributes won’t matter, right? I know, I know.”
Ashtaroth, who was explaining diligently, was interrupted. The ability is something I know from games. 
If it has a similar power in reality, the Old God with all resistances would be more user-friendly. Damage reduction skills ultimately prove effective.
“Didn’t your parents teach you not to interrupt when someone is explaining something?”
“Yeah. Honest Mii-chan has never interrupted papa and mama’s conversations! Is there even a right time to teach that?”
Tilting her head curiously, I asked, and Ashtaroth nodded in response.
“Indeed, there isn’t. It’s only when you’re interrupting someone else’s conversation… Well then, remember the souvenir from the underworld. Don’t interrupt people’s conversations!”
“It’s fine if it’s a Demon God. Got it!”
“…Enough talk! Know this power of mine!”
[Elemental Body Transformation]
For some reason, Ashtaroth gave up on talking with Miu and started circulating magic within its body. The Demon God’s body mixed the power of various elements, transforming into an energy body that combined them.
In its transformed state, Ashtaroth emitted a formidable power by merely existing, warping space, melting the floor with extremely high-temperature energy, and crushing the ceiling finely.
Ashtaroth had transformed not into a physical form but into a vast energy body.
“[Final Form] of mine—”
“If you deal damage, the attacker also gets hurt. Instead of transforming like in a game, you’re in your final form from the beginning. You’re a careful Demon God.”
“That’s right!”
For some reason, Ashtaroth became displeased. Well then, let’s stop teasing him. From now on, Miu will take it seriously.
As the cries of crow echoed from somewhere, the analysis results were projected before me.
-True Ashtaroth: Level 185, Resistance: All Elements-
Nice. That’s what a hidden boss is supposed to be. It’s worth the fight.
“Well then, shall Mii-chan show her true form too?”
[Old God Form]
Facing the final form of Ashtaroth, Miu puffed out her chest proudly, closed her eyes, and circulated magic throughout her body.
From her fingertips to the tips of her toes, a power that felt cold, and empty flowed, and a quiet power dwelled in her body.
Without emitting an explosive aura and without changing her appearance, Miu was clearly different from earlier. She floated slightly from the floor, completing her transformation.
When I smoothly opened my eyes, calm ice-blue eyes reflected Ashtaroth.
“This is my second-stage transformation before achieving complete synchronization.”
“…W-Why are you erasing space? Your power…”
“The [Old God Form] is a bit inconvenient. It’s passive and causes damage to the surroundings. In the game, it got labeled as [Chaos]. It has a weakness in that it can only be used solo because it affects the party too.”
I calmly informed the retreating Ashtaroth, who was now frightened and stepping back. This is the true meaning of being the strongest solo player. Parties are meaningless, and everything can be handled alone. That’s what it means to be an Old God.
Everything around Miu began to disappear as if being erased from space. The standing floor and the ceiling seemed as if they never existed in the first place, with no dust present, and everything was disappearing.
Miu’s surroundings vanished completely in a spherical shape.
Miu’s current stats had already surpassed human limits. The Old God didn’t even have a ☆ mark.