Meaning

To face matters openly, with dignity, with no need to hide or shrink. The doubled kanji emphasise unwavering bearing.

恐れることなく、立派で誇り高い態度で物事に臨むこと。

The Kyojuro Rengoku line

Verbatim from the source article

「胸を張って生きろ」

"STAND TALL AND BE PROUD."

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Why it fits Kyojuro Rengoku

The imperative "live with your chest out" is the body-language form of dōdō-seisei. Rengoku says it to Tanjiro, but it is also how he himself stands in every panel — open posture, gaze level, no flinch.

Sources

• デジタル大辞泉 — 正々堂々 (dictionary)
• 精選版 日本国語大辞典 — 正々堂々 (dictionary)

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