The comic plot of Fonzy is outrageous, but to writer-director Isabelle Doval, it's just an armature that supports its gently funny characters and its themes of emotional and filial connections. Diego, played by the pleasantly Robert Downey Jr.–like José Garcia, is an affable fuckup with big debts to loan sharks and a family reputation of extreme unreliability. But he excels at producing unbelievably potent sperm, gallons of which he sold, during his twenties, to a fertility clinic, to supplement his intermittent income. Eighteen years later, after the sperm bank is forced to issue a consanguinity warning for inadvertently administering too much of his sperm to a single community, Diego discovers that he is the biological father of 533 children. 150 of them have filed a lawsuit to overturn the clinic's confidentiality agreement and learn the identity of "Fonzy," their anonymous paterfamilias.
Through the courts, Diego receives bios of these 150 kids, and begins visiting them, anonymously, to see what they're like: He finds artists, students, various kinds of performers, rebels, and introverts, who, having met one another, have formed a large social group that consists entirely of siblings. Doval includes a few over-the-top characters among the gentler souls -- Diego's lawyer, his pregnant fiancée, and one flamboyant, brooding test-tube progeny -- whose functions are to articulate the crazy parts and move the story forward. This leaves Garcia free to evolve Diego from an extended adolescence and become man enough to face the world and say, "Je suis Fonzy!"