Great Collapse
Within a blue-tinged world, with thousands of wandering souls, Michael announces his entrance by literally tearing a hole into the realm with the help of Tiffania's stolen Dimension Gate spell. "I'm here to get my dragon back! Anyone who gets in my way gets their soul eaten!"
...
The few ghosts who'd been standing in the area instantly scatter, screaming and running from the madman who thought he could endure the wrath of the Ideal Masters. This was the correct decision, as not a moment later a huge torrent of soul energy crashes into the spot where Michael was standing, the blue-purple light searing a wretched hole in reality itself and literally disintegrating any spirit stupid enough to be nearby.
Once the light clears all that is left in the area it struck is a purple boiling cracked ground and oozed a dangerous violet light... Along with a single figure.
Michael wipes his mouth and lets out a burp, "Man, if I knew you guys were just going to shoot soul energy at me, I'd have come much sooner!" he laughs.
The energy they'd fired was an extremely concentrated form of energy they'd extracted from the souls of their victims. To any other being, Daedric Princes included, it would be incredibly caustic and dangerous... But for Michael, who'd maxed out [Necromastery], it was like dunking his head in a pool of cola, very refreshing.
"Oooh, I'm buzzin'!" he says shaking his hands, feeling as if he was on a sugar high. "Alright, come out and fight me or I'll just directly merge my realm with yours! I guarantee that shit won't go well for you!"
...
The world around Michael warps and distorts, turning into a white plain that seemed to go on endlessly. Then, hundreds of figures began appearing around him, each looking like a silhouette made of purple diamonds with no other discernable features.
"INVADER, WHY HAVE YOU COME!?" they all simultaneously demand.
"I told you earlier! You stole my dragon! Give him back or I'll take this place apart, piece by piece!"
"THE SOUL IS OOURRSSSS!!!!"
Michael taps his foot impatiently, "How about we play a game? I'll give you three hours to kill me. I'll do absolutely nothing but stand here and nothing else. If you fail, you'll not only give me back Durnehviir, but I want every single soul you have in your possessions. Every last one... So, how about it? Deal?" he asks, his voice distorting slightly as he asks the last question.
...
"WE REFUSE."
Michael shakes his head, "I don't think you properly understand..." he reaches his arm out and clenches his fist, pulling on the thread that connects his soul to his realm. The air crackles around him and soon shatters, creating a window which reveals The Floating Isles of Providence to the Ideal Masters.
They let out inhuman growls at this but don't immediately make a move, so dangerous were Michael's actions that distracting him now could doom their entire realm... Due to Tiffnia's stolen void spell, he was essentially doing what Molag Bal tried to do to Tamriel all those years ago... Except he didn't require all the preparation, sacrifices, rituals, etc... With a flick of his hand he could do what Molag Bal could not over many centuries of planning.
"So I'll ask again, politely, do we have a deal?"
...
"THE TERMS. WHAT DO WE GAIN?"
"I thought not killing you all was enough but... How about my soul and the souls of everyone in my realm? That a good enough reward for you?"
"YES." they agree to the deal, inadvertently activating Michael's concepts and all jumping into action.
Since their soul energy attack obviously wouldn't work, they begun attempting different methods. Strangely to Michael, they began using Tamrielic magic against him, spells that one could learn. Indeed, the Ideal Masters were far magically stronger than any other mage he'd come across... Even Savos and the Psijic Order mage hadn't had an ounce of the power they were exerting against him now.
His body was incredibly magically resistant, but the deal allowed the Masters to get... Creative. They spent an hour condensing magical energy into what was essentially a bomb, one that had the same power as a couple nuclear bombs... They shoved this down his throat, and detonated it.
He wasn't durable enough to endure a nuclear explosion in his stomach... He died. But... Not really, his concept of death allowed him to recognise the true sense of the word and use it in his agreement, true death was permanent, so the binding snapped back into place when his body reformed itself in the Ideal Master's midst, surprising them all rather severely.
They made a few more attempts to kill him, but quickly realise that they'd been tricked. Then, they began panicking. Their realm trembling as the realisation of the situation hit them. Michael hadn't understood the implications of his deal until after it'd concluded, the fact that the realm of the Ideal Masters was entirely formed from soul energy.
This meant that if all of their souls were claimed, their realm would literally collapse in on itself. It would implode into nothingness, another unclaimed and unattributed realm amongst the other trillions in Oblivion.
Once the deal was concluded the Ideal Mastera all began bursting into particles around him, their own souls being claimed and thrown into the hellish portion of Floating Isles of Providence.
Before the Soul Cairne begins collapsing however, Michael grips it and binds it to himself, unwilling to let an already furnished property to go waste. Not to mention the fact that all black soul gems were linked to it, along with any soul used from said gems... In mortal terms, the realm was akin to a vending machine for Michael, allowing him to occasionally come back and collect the profit of souls.