  We propose that the dynamics of a scalar $\phi$ of mass $O(10)$ MeV that is
weakly coupled to the Higgs can lead to a first order electroweak phase
transition, fulfilling a key requirement for baryogenesis. Stability of the
model near the weak scale requires a suppressed - possibly vanishing - top
Yukawa coupling to the Higgs before the transition which rises to the Standard
Model value afterwards. This can be accomplished through the dynamics of $\phi$
via a dimension-5 operator. We conjecture that the entire Standard Model flavor
structure could turn on, mutatis mutandis, after the electroweak phase
transition, via dimension-5 interactions of $\phi$ suppressed by scales ranging
from $O(10^3)$ TeV to near Planck mass. Due to its suppressed couplings, $\phi$
is long-lived and can lead to missing energy signals in rare kaon decays, which
can be probed by the KOTO experiment.
