Lol okay so I read a lot of this pairing and it's basically just elemental chaos theory in written form. Cinderace is all fire and speed, right? Pure offense. Lucario's this tactical, aura-reading sentinel. The fics I've saved tend to use that difference to build tension – a Cinderace who charges in without thinking, a Lucario who has to constantly pull them back from the edge, maybe literally shielding them with a Bone Rush barrier when an Ember gets wild. You get scenes where Lucario is trying to meditate and sense disturbances, but Cinderace's restless energy keeps disrupting the aura field, which writers use for comedy or for showing how they learn to sync up. It's a classic opposites-attract framework, but with the added layer of one being physically fragile compared to the other's steel typing, which invites a lot of protective tropes. I skim anything that turns it into a boring power-level debate, though. The good stuff is about how they communicate through fighting styles, not who would win in a straight battle.
The contrast in their powers often ends up mirroring their personalities in these stories. A Cinderace who is brash and impulsive finds their usual 'run and gun' style ineffective against an opponent that requires more strategy, forcing them to slow down and actually listen to their partner's tactical aura-sense. Meanwhile, Lucario learns to incorporate that unpredictable, fiery spontaneity into their own more rigid patterns. I remember one fic where they trained together, and Lucario started using Cinderace's Pyro Balls as moving targets to practice Aura Sphere accuracy. It was a neat way to show their synergy developing beyond just romantic tension.