expression, godan verb (-ku)
let down one's guard; relax one's guard
Used when someone becomes less cautious or vigilant, often after feeling safe or comfortable.
彼は親しくなるとすぐに警戒心を解く。
He quickly lets down his guard once he gets to know someone.
相手が笑顔を見せたので、警
Because the other person smiled, I let my guard down.