Nick Movies has decided to believe in “Unicorn,” buying Joe Aucoin’s comedy fantasy spec and setting it up with producer John Jacobs at his Smart Entertainment shingle.Story’s centers on a workaholic single father in Manhattan, who has to deal with his 5-year-old daughter’s desire for a unicorn of her own. Smart Entertainment’s Colin O’Reilly will exec produce. Aucoin previously sold his romantic comedy spec “K Thru 12” to New Line. Jacobs most recently produced DreamWorks’ “Blades of Glory,” starring Will Ferrell and Jon Heder. Ben Stiller and Stuart Cornfeld’s Red Hour also produced the high-concept comedy set in the world of professional ice skating.