Meaning

As fast as lightning, as quick as the spark struck from a flint — action so rapid that an opponent has no time to respond.

稲妻の光や石を打った時の火花のように、行動や動作が非常に素早いこと。

The Kyojuro Rengoku moment

無限列車内を駆け巡る圧倒的なスピード — Inside the moving train, Rengoku covers every carriage faster than the demon can blink, suppressing the dream-trap creatures before they can fully manifest.

Why it fits Kyojuro Rengoku

A Hashira's combat speed is not metaphor in Demon Slayer — and Rengoku's Flame Breathing forms read in the manga panels as literal flashes of light, the technique's afterimage filling the gutter while the body has already moved.

Sources

• デジタル大辞泉 — 電光石火 (dictionary)
• 精選版 日本国語大辞典 — 電光石火 (dictionary)

How these sources are vetted →