Meaning

To hold neither one's body nor one's life as worth sparing when the cause demands it — the Buddhist ideal of dharma-protection through self-sacrifice.

仏道や大義のために、自分の身や命を全く惜しまないこと。

The Kyojuro Rengoku moment

致命傷を負っても猗窩座を逃さない執念 — Half-pierced through the chest, Rengoku grips Akaza's arm into the wound so the demon cannot retreat before the sun finishes him.

Why it fits Kyojuro Rengoku

The most-quoted image from the Mugen Train arc — Rengoku's hand on Akaza's wrist as the sky lightens — is fushaku-shinmyō in literal staging. He has already lost the body; he refuses to release the larger fight while there is breath left.

Cultural note

Origin in classical / Buddhist / Confucian tradition

A core vow in the Lotus Sutra and in Mahayana Buddhist literature on bodhisattva conduct.

Sources

• デジタル大辞泉 — 不惜身命 (dictionary)
• 精選版 日本国語大辞典 — 不惜身命 (dictionary)

How these sources are vetted →