Meaning

A will that will neither bend (撓) nor yield (屈), no matter the difficulty or setback. The doubled negation emphasises absolute resistance.

強い意志を持ち、どんな困難や挫折にも決して心が折れないこと。

The Kyojuro Rengoku line

Verbatim from the source article

「心を燃やせ歯を喰いしばって前を向け」

"KEEP YOUR HEART BURNING, GRIT YOUR TEETH AND MOVE FORWARD."

Read the full breakdown →

Why it fits Kyojuro Rengoku

Rengoku's catchphrase "Keep your heart burning" is the modern Japanese voicing of this ancient idiom. The phrase comes from his dying breath but he repeats it as a teaching — a virtue meant to be inherited by those who survive him.

Kanji breakdown

The four characters, one by one

• 不
  4 strokes Grade 4 JLPT N4 #101 most common

  Not

  音 On

  ふ · ぶ

  Radicals

  Not

• 撓
  15 strokes

  Bend · Train · Lithe

  音 On

  とう · きょう · こう · じょう

  訓 Kun

  たわ.む · しな.う · しお.る · たわ.める · みだ.す · みだ.れる

• 不
  4 strokes Grade 4 JLPT N4 #101 most common

  Not

  音 On

  ふ · ぶ

  Radicals

  Not

• 屈
  8 strokes JLPT N1 #1434 most common

  Yield

  音 On

  くつ

  訓 Kun

  かが.む · かが.める

  Radicals

  Flag · Exit

Cultural note

Origin in classical / Buddhist / Confucian tradition

From classical Chinese texts about scholar-officials who refused to bend under political persecution. The bookend doubling — 不…不… — is a classical rhetorical device emphasising totality.

Sources

• デジタル大辞泉 — 不撓不屈 (dictionary)
• 精選版 日本国語大辞典 — 不撓不屈 (dictionary)

How these sources are vetted →