Play word 一増一減 一増一減 いちぞういちげん 16,800,000-year period over which a human lifespan increases from ten years to 84,000 years (by one year per century) and then decreases back to ten (by one year per century)
Play word 一足一刀 一足一刀 いっそくいっとう distance in sword combat where approaching one more step allows hitting one's opponent