I'm always surprised this triad isn't more common given how rich the character dynamics are. A classic set-up I've seen a bunch has Midoriya's analysis brain figuring out Bakugou's bravado and Todoroki's restraint actually mirror each other in weird ways—both are trapped by expectations and pasts they're trying to outrun, just with opposite presentations. That often kicks off a plot where Izuku becomes the unintentional bridge between them, usually after some joint training incident or shared detention. It can feel a bit tropey, but when the writer nails the slow, grudging shift from rivals to something more, the tension is unreal. You get Bakugou's explosive vulnerability and Shouto's quiet intensity bouncing off Deku's relentless empathy in ways that just don't work in a standard pairing.
A personal favorite angle is the 'reluctant co-parenting' scenario, where some outside force—a kid, a pet, a sentient quirk manifestation—gets dumped on them and they have to figure it out together. It forces a domesticity that's completely foreign to all three, especially Katsuki, and watching them stumble through building a home is weirdly touching. The best ones don't rush the romance; they let the care develop from shared responsibility and stupid arguments over grocery shopping.
There's also a subset that leans hard into the 'wounds that match' idea, exploring how their shared trauma from the UA war arc or individual battles could lead to a specific kind of understanding. These get heavy, dealing with nightmares and panic attacks and the weird comfort of being with people who get it without needing it spelled out. They're not always happy reads, but they feel earned.