Movies about single guys who become suddenly burdened with the responsibilities of parenthood, whether from Hollywood ("Three Men and a Baby") or Japan (the underrated "Yukai Rapusodi [Accidental Kidnapper]"), follow a pattern set in stone: After rising to various patience- and character-testing occasions, the new caregiver not only bonds with his charge, but becomes something of a fatherly role model. It would be a major violation of movie law for the hero to quietly give up the kid and breathe a sigh of relief.

So it mostly is with "Usagi Doroppu" ("Bunny Drop") by Sabu (born Hiroyuki Tanaka), the lanky actor-turned-director known for frenetic films, beginning with 1996's "Dangan Ranna (Non-Stop)," in which the harassed hero runs the equivalent of a marathon. Based on a popular comic by Yumi Unita, "Bunny Drop" departs slightly from formula in that the 30-year-old salaryman hero, Daikichi (Kenichi Matsuyama), actually volunteers to raise 6-year-old Rin (Mana Ashida), the love child of his recently deceased grandfather.

The opening scenes, in which Daikichi makes his momentous decision and begins his adventure in fatherhood, set the story into motion with maximum velocity and minimum wasted motion. Cutting back and forth between the grandfather's funeral, at which cold-hearted relatives talk about Rin as if she were an inconvenience, and Daikichi's bumbles and stumbles in his new life with her (including mad dashes to get her to the day-care center on time), Sabu deftly treads (or rather sprints along) the middle line between the dramatic and comic, while making us understand why a free-as-a-bird single guy would choose to take on a kid who is essentially a stranger.