Cpt Asuna, the Callous Heart

You may choose not to untap Asuna, the Callous Heart during your untap step.
{2}, {t}: Target opponent puts a -1/-1 counter on target creature he or she controls. If they can't, Asuna, the Callous Heart deals 2 damage to him or her instead.
{2}, {ut}: Destroy target creature with a -1/-1 counter on it.