To brace oneself or get mentally prepared; to take up a stance. Somewhat literary/rare in modern usage. See noun '気構え'.
試合前に深呼吸して気構えた。
I took a deep breath and mentally prepared myself before the match.
彼はいつもすぐに対応できるように気構えている。
He always steadies himself so he can respond immediately.
面接では落ち着いて気構えることが大切だ。
It's important to stay calm and brace yourself during an interview.