How to say "fiercely" in Japanese

• ぼんぼん
  adverb (with と)Covers fiercely of a fire burning: an onomatopoeia evoking flames crackling and blazing up. Use it of the fire itself, not of a person's manner or temper.
  火ひがぼんぼん燃もえている。↗

  The fire is burning furiously.
• 猛然もうぜん
  adverb (with と), taru-adjectiveCovers fiercely of manner and behavior: someone attacking, charging, or pressing forward ferociously or furiously, often with fierce resolve. It describes fierce human action, not burning fires.
  犬いぬが侵入者しんにゅうしゃに猛然もうぜんと吠ほえかかった。↗

  The dogs barked furiously at the intruder.
• ボーボー
  adverb (with と)Also covers fiercely of burning: an onomatopoeia for flames leaping up vigorously, a fire burning furiously. Like ぼんぼん it depicts the blaze itself, with an image of flames roaring high.
• ここを先途とここをせんどと
  expression, adverbCovers fiercely as 'desperately, with full resolve': a less common set phrase for fighting or striving as though this moment were the decisive one. It describes all-out, wholehearted effort, not flames or heat.
• カンカン
  adverb (with と)Covers fiercely of shining: an onomatopoeia for light or heat blazing intensely, the sun beating down fiercely. Use it for blazing sunshine or intense heat, not for people's manner or fighting spirit.

Pick by what is fierce: 「ぼんぼん」 and 「ボーボー」 describe fire burning hard, 「カンカン」 fierce shining heat, 猛然 a ferocious manner or attack, and 「ここを先途と」 desperate, wholehearted resolve.

Usage comparisons are AI-assisted and cross-checked by multiple models; for study reference only

• ぼんぼんfiercely (e.g. of a fire burning)
• 猛然もうぜんfiercely
• ぼうぼうvigorously (burning)
• ここを先途とここをせんどとfervently
• かんかんfiercely (shine)
• はたとsharply (glance, glare, etc.)
• 丁々発止ちょうちょうはっし(arguing) fiercely