Very fierce or intense (e.g., a fight or competition); severe, hard-fought, or cutthroat.
ライバル会社との市場争いは熾烈を極めている。
The market battle with the rival company has become extremely fierce.
選挙戦は熾烈になり、候補者たちは毎日演説を続けた。
The election campaign grew intense, and the candidates gave speeches every day.
その試合は熾烈な攻防で観客を沸かせた。
That match thrilled the audience with fierce back-and-forth action.