Genuinely, the dynamic between these two is so untapped? It's all about that supreme cosmic ego clashing. One plot I'd kill to read would center on the Heian era, before Sukuna became the 'King of Curses' and while Mahoraga was still a revered, unbroken shikigami of the Zen'in clan. Think of it as a tragedy of mutual fascination—Sukuna encounters this 'perfect' adaptation during a slaughter and becomes obsessed not with destroying it, but with understanding its core. He'd try to corrupt it, to prove even ultimate adaptation can be bent to a will like his. It wouldn't be romance, more a horrifying symbiosis where Mahoraga slowly adapts to Sukuna's chaotic cursed energy, becoming something new and terrifying together. The ending writes itself: the first time Mahoraga 'adapts' not to defeat a threat, but to fulfill a desire of Sukuna's, breaking its own fundamental nature. That's the moment it truly becomes 'his'.
Another angle is post-Shinjuku Showdown, if you buy into theories about Sukuna's lingering consciousness or a binding vow remnant. Imagine Mahoraga, somehow restored or imprinted, wandering with a shred of Sukuna's will. Not a possession, but a fusion—a being that adapts relentlessly but is driven by that kingly arrogance. They'd be this force of nature, upending both jujutsu and curse societies, challenging Gojo's legacy from beyond the grave. The conflict would be internal: is this new thing Mahoraga using Sukuna's memories, or is it Sukuna wearing Mahoraga like the ultimate suit of armor? The philosophical weight of identity there is massive.