I'm not even sure what the appeal is, honestly. Their dynamic is pure animosity on screen, so building tension means stretching the premise until it snaps. It's not a natural ship, so you've got to manufacture reasons for them to interact. Maybe a shared mission, or a scenario where they're forced to rely on each other. But the real challenge is avoiding making either one OOC. Bakugou's explosive pride and Toga's obsessive, chaotic affection are fundamentally incompatible. You can't have him suddenly being gentle or her being rational.
A method I've seen work is leaning into that incompatibility as the source of tension. It's not romantic tension, it's the raw, gnawing tension of two live wires sparking against each other. Every interaction is a power struggle. He sees her as a villainous pest; she sees his rage as something beautiful and intense to covet. The tension comes from whether that fascination curdles into something else, or if it just ends in violence. It's a high-wire act.
You'd need to play with perspectives too. A scene from his POV would be all disgust and tactical assessment. From hers, it might be a twisted admiration of his 'cute' angry face. That gap itself creates narrative tension for the reader, who's waiting to see if those perspectives ever align, even for a second. I'd keep any physical moments fraught with danger—a grabbed wrist that's as much a threat as a connection, a shared secret that binds them in mutual blackmail.
Honestly, writing it feels like trying to balance a lit stick of dynamite on a knife edge. It's not a comfortable read, and it shouldn't be. The best fics in this tag embrace that unsettling, almost predatory vibe. The 'will they, won't they' is secondary to 'will one of them finally snap and try to kill the other?' That's the core tension.