The ending, called 'hako tataki' (hitting the box), expresses Mitsuhide's decision to rebel, so much for being a loyal retainer, by taking the box afresh (or hitting the box).
幕切れの「箱叩き」では、光秀がもうこれまでと謀反の心を、箱を持ち直す（または箱を叩く）ことで表す。