忽然

こつぜん【忽然】

●忽然と(して) suddenly; all of a sudden; all at once; in an instant; in a flash; unexpectedly; abruptly

・忽然と姿を消す vanish [disappear] as if by magic; vanish into thin air

・忽然として来たり忽然として去った. He vanished as suddenly as he had appeared.