A proverb meaning to make something already strong even stronger (literally 'an iron club for an ogre'); to give someone an unbeatable advantage.
彼がチームに入れば、エースにさらに力を与える。まさに鬼に金棒だ。
If he joins the team, he'll make the ace even stronger—truly adding a metal rod to an ogre.
最新のソフトを導入すれば、会社の業務効率は鬼に金棒だ。
Introducing the latest software will make the company's efficiency even better—like giving an ogre a metal rod.
優秀なコーチがついて、選手たちは鬼に金棒の状態だ。
With an excellent coach, the players are in a '鬼に金棒' situation.