Meet Yukawa Reona, a genius with a brain like a supercomputer. He's shy, awkward, and the kind of guy who disappears in a crowd, but he's got a hopeless crush on one girl. Unfortunately, her type is tall guys. "If I don't do something, I'll never be Shizu-nee's man! Gotta get taller, no matter what!" Using his big brain, he cooks up "Senobitan Z"--a crazy growth serum that's supposed to make him shoot up like a weed. But when he drinks it... he gets a weird side effect. Instead of getting taller, he shrinks into a kid, but only when he gets turned on. And that's not all! Every time he nuts, he grows back... and gains a tiny bit of height. Now, stuck in his "kid mode," he's accidentally triggering every woman's mommy instincts seducing busty babes and knocking them up left and right! The baby-making spree starts now!