Poriferan Duel: Kenpachi Shizuma vs. Spinge-Zuma refers to the first battle between captain-turned-Sternritter Kenpachi Shizuma and his progeny, the sorcerous Spinge-Zuma. Taking place within the extradimensional realm known as the Void, it was a battle to determine who was the most yellow and porous being of them all.
After emerging from the Void following Yhwach's defeat, Spinge-Zuma wished to seek out the two beings he saw as responsible for his existence: Kazuya Kurotsuchi, who actually created him, and Kenpachi Shizuma, the man whose spiritual essence was used to create him. Wanting to prove himself the better of the two men, Spinge-Zuma banished the realm of Equestria to the Void in order to draw out both men, who he knew were closeted bronies. Shizuma, using his transcendent speed, appeared before his progeny. Swearing to avenge Twilight Sparkle, Shizuma challenged his spawn to a duel within the Void. Spinge-Zuma agreed.
After traveling deep within the Void at speeds faster than mortals can comprehend, Spinge-Zuma began to taunt his progenitor, claiming that all the things that supposedly made Shizuma great disappeared once he tossed away his life as a Shinigami. He further states that all these things now belonged to the Void. Shizuma retorted by stating that Spinge-Zuma should just marry the Void if he loved it so much, to which the warlock answers that he'd already attempted it twice.
Shizuma draws his Zanpakutō, Gott no Kami, and tells his spawn that he will soon be married to the ground. He fires a Getsuga Tenshō which undoes and restarts all of creation before Spinge-Zuma swipes it away, telling the former captain that it's pointless. Reaffirming that all things will eventually return to the Void and that even a being as mighty as Shizuma would eventually disappear as well, Spinge-Zuma summons the dragon Bahamut to destroy Shizuma. Bahamut uses Mega Flare on Shizuma, only for the Sternritter to utter "Cute." and use The Porous to absorb the blast. Shizuma fires it back at Spinge-Zuma, who again asserts that it's futile.
Spinge-Zuma opens a portal and the blast passes into it, eventually hitting and destroying the city of Metropolis, causing the citizens to groan and note that at least it was a bad guy who destroyed their city this time.
Shizuma fires a Heilig Pfeil at his progeny, only for the warlock to open another portal, where it strikes and destroys the home of a silver-haired martial artist. A bearded fellow wearing an Eevee shirt walks by and notes that it's karma for being a bad person before giving the martial artist a wedgie.
Shizuma finally decides to put an end to the nonsense by activating his Quincy: Vollständig, Dirtydaniel. Using his harp, he absorbs Bahamut, Spinge-Zuma and much of the Void before expelling them in a violent burst, sending the warlock even deeper into the Void. Before vanishing, Spinge-Zuma mocks him once more, telling him that he has seen realities where the former captain is nothing more than a mere fry cook. Shizuma dismisses the idea as being ridiculous before banishing his progeny to the inner depths of the Void.
Shizuma returns to the material world, noting that the encounter was far more irritating than he thought it would be. He curses Spinge-Zuma for banishing innocent ponies and vows to bring them back.
Elsewhere, Spinge-Zuma notes how inconvenient it is to be so far within the Void, to the point where he barely recognizes the landscape. A voice calls out to him, telling the warlock that he is quite fortunate as few have remained in his realm for as long as he had without going mad. The voice identifies itself as being Dormammu, the lord of the Dark Dimension, who offers to aid Spinge-Zuma in gaining his revenge. The warlock chuckles, noting that the fun has only just begun.