兜の緒を締める（かぶとのおをしめる）

Japanese vocabulary

Meaning: to brace oneself (e.g. for battle); to pull oneself together; to focus one's mind; to tighten the strings of one's helmet

See it used in real works

• Example sentences from Japanese novels & web fiction (Massif)
• Hear “兜の緒を締める” pronounced in real videos (YouGlish)