The Elder Lich laughed with deep fury upon hearing Seran's response, rattling its bone staff as it called forth more green fireballs from the miasma, "Say that again, brat, after you survive!" With a flick of its staff's bone topper, a wave of fireballs charged towards the white-haired boy, who was forced to dodge and evade as rapidly as possible. The Elder Lich flung one bony hand toward the miasma beside it and sucked a great deal into an orb shape before wrapping it in green flame and throwing it like a regular fireball at Seran.
Seran might be immune to elemental magic, but he wasn't immune to the physical force that came with each attack, and just a pair of fireballs earlier nearly caused him to lose his footing completely. Using his sword, whatever attacks he didn't manage to dodge, he cut through with space magic. The Elder Lich's miasma orb fireball was one of them, as it had cast another wave of fireballs with it. Upon cutting through the fireball and sensing what felt like a membrane being broken, the white-haired boy cussed as he dropped the sword and jumped as far back as he could. The sword corroded into rust near instantly as the contained miasma erupted. So condensed was the miasma that it looked to be a tidal wave of green-black poison as it surged towards the young demigod.
Drawing in more of the miasma, which had now lessened by a good amount, the Elder Lich devoured and converted it into more mana. With powerful spells, it summoned heavy full-body plate armor made of death magic, and its staff transformed into a large shadowy scythe. Using its remaining mana and absorbing more from the miasma to empower itself, the Elder Lich teleported towards Seran.
"Son of a bitch, this bastard is hard to kill," hissed the white-haired demigod as he hastily summoned a life magic barrier around him. The tidal wave of liquid-esque miasma crashed into the barrier like a bulldozer, nearly shattering it from the impact alone. On top of that, the corrosion power it had continued to attack the cracks in the barrier in an attempt to seep through. It managed to hold on until the end of the surge but failed to withstand the powerful scythe blow of the Elder Lich who appeared behind the wave. Seran yowled in pain as the magic blade cut a long gash from his right shoulder to his left hip. The biggest pain he received wasn't from the cut, but from the scythe's deathly power, feeling like acid was being poured into his wound and into his bones.
[Shit, I didn't sense him appear with all of that miasma in the way! Hold on, let me clear up that power... how did it bypass the immunity?] William panicked at realizing that Seran had taken a nasty injury due to having their senses fooled, and he used a curative spell to remove the scythe's power from the wound, which then healed rapidly from his Semi-Immortality ability. Still, the scythe's blade had to have been formed from death magic, which Seran is immune to. For such a weapon to ignore his immunity and deal considerable damage to his body, the Elder Lich definitely knew some tricks.
Seran released a pent-up breath after he felt the acidic pain leave his body, quickly withdrawing Yggdrasil's Comet again to defend against the scythe as the Elder Lich attacked again. The meteoric blade proved too much for the deathly scythe to sever and corrode, making it Seran's best counter to it. Still, he had trouble dealing with the onslaught of powerful scythe attacks and numerous green fireballs that the Elder Lich kept casting, and it was all he could do to block the scythe alone and let William handle the fireballs with space magic rifts.
The Elder Lich's eye flames still burned with anger, though it was now mixed with a gloating pride as it continued to slash and slice the enormous scythe at the boy, who it was surprised to realize had an item capable of surviving several strikes from the scythe. Whenever the demigod did manage to find an opportunity to strike back, the plate armor and constant attacks made each attempt into nothing more than a scratch due to how rushed he was to defend himself again. Dozens of subsequent cuts marked Seran's body as the two remained locked in mortal combat, with the Elder Lich's plate armor and scythe seeming to have taken no damage at all.
As this was happening, William was still trying to analyze the ability that the Elder Lich was using, going through all of the data he could possibly find. [I got it! That's not death magic he's using! That's devil magic from the Abyss!] He checked his data twice, thrice, even five times to be sure he wasn't getting it wrong. [This Elder Lich is using the devil magic that the Sixth Devil King used! The miasma is all death and devil magic designed to devour all life and turn it into the caster's power, which can then be used to empower them!]
Seran's eyes flickered with shock as he nearly shouted, "What!?" He quickly teleported backward about 5m before defending himself again. "Devil magic? You're sure?"
[Positive! There is miasma-based death magic, but none of their spells could bypass your immunity. It would have to be either divine in nature or from another source, namely the devils. This is certainly not divine magic, so it has to be devil magic! We don't have anything to handle devil magic. You have to kill the Elder Lich now!] William's urgency filled every word as the danger of the unique magic of devils became more and more prevalent. Divine magic wasn't available for mortals, and for Seran it had one of the lowest chances of appearing in his Gacha draws. Angels were the only other beings that could use Divine magic, but they haven't appeared on Aregard since the Abyss Invasion.
The skeletal devil laughed wickedly, "I didn't expect a child in this day and age to recognize my magic! Not that you can do anything about it though. No mortal can withstand my devil magic!" It continued to cast green fireballs at the boy, who could only defend himself with space rifts now.
[Seran! Stop defending, leave that to me! Destroy its head! It's undead now, so destroying its head will crush its soul!]
Seran growled and began pouring tons of mana into his guandao blade, infusing it with all of the elements he could at once, as it was the best he could do to mimic a divine spell. Lowering himself into a thrusting stance, the white-haired demigod hissed, "I can't enjoy this fight any longer. You're too dangerous to leave alone." He made a silent apology to the tomb as he charged forward with as much speed as he could muster.
All of the miasma was gone now, and all that remained was the power holding the plate armor together and the overwhelming strength empowering the scythe. The Elder Lich also charged power into its scythe and swung it with its full physical capabilities, space ripping and tearing as it was cut by the blade. The devilish magic weapon collided with the demigod's guandao thrust with full force, both fighters putting their entire body into their attacks in an attempt to overpower the other.
In the end, the Elder Lich's strength weakened against Seran's Infinity ability, and the scythe blade was shattered by the guandao as it crashed into the plate armor helmet, the magic strength breaking the summoned armor and obliterating the Elder Lich's skull as its howl of rage was silenced.