I'm not aware of a Magic: The Gathering keyword or ability called "Fira." It's possible this is a misspelling, a card name, or something from another game entirely.
You might be thinking of a few similarly-named things:
- Fear — a keyword meaning a creature can only be blocked by artifact creatures and/or black creatures.
- First strike — deals combat damage before creatures without it.
- Flying — can only be blocked by creatures with flying or reach.
- Fira — this is actually a fire spell from the Final Fantasy series, not Magic. (Though with Universes Beyond sets, Final Fantasy cards now exist in Magic, so it may appear as a card name.)
If you can clarify the exact card or term—or its spelling—I'll happily give you a precise rundown of what it does, the common rules trap, and how it plays in Commander.