Don't look back.
Ushiro o furikaeru na.
back; behind; rear
indicates direct object of action; indicates subject of causative expression; indicates an area traversed; indicates time (period) over which action takes place; indicates point of departure or separation of action; indicates object of desire, like, hate, etc.
to turn head; to look over one's shoulder; to turn around; to look back; to think back (on); to reminisce; to look back (on); to reflect (on)
(sentence end, mainly masc.) indicates emotion or emphasis; (used with masu stem verb) command; (used with dictionary form verb) prohibition