  \object{SN 2021aefx} is a normal Type Ia Supernova (SN) with red excess
emission over the first $\sim$ 2 days. We present detailed analysis of this SN
using our high-cadence KMTNet multi-band photometry, spectroscopy, and publicly
available data. We provide the first measurements of its epochs of explosion
(MJD 59529.32 $\pm$ 0.16) as well as ``first light'' (MJD 59529.85 $\pm$ 0.55)
associated with the main ejecta ${\rm{^{56}Ni}}$ distribution. This places our
first detection of SN 2021aefx at $\sim -$0.5 hours since ``first light'',
indicating the presence of additional power sources. Our peak-spectrum confirms
its Type Ia sub-classification as intermediate between Core-Normal and
Broad-Line, and we estimate the ejecta mass to be $\sim$ 1.34 $M_{\odot}$. The
pre-peak spectral evolution identifies fast-expanding material reaching $>$
40,000 km s$^{-1}$ (the fastest ever observed in Type Ia SNe) and at least two
distinct homologously-expanding ejecta components: (1) a normal-velocity
(12,400 km s$^{-1}$) component consistent with the typical photospheric
evolution of Chandrasekhar-mass ejecta; and (2) a high-velocity (23,500 km
s$^{-1}$) component visible during the first $\sim$ 3.6 days post-explosion,
which locates the component within the outer $<$ 16\% of the ejecta mass.
Asymmetric, subsonic explosion processes producing a non-spherical photosphere
provide an explanation for the simultaneous presence of the two components, as
well as the red excess emission via a slight ${\rm{^{56}Ni}}$ enrichment in the
outer $\sim$ 0.5\% of the ejecta mass. Our spectrum from 300 days post-peak
advances the constraint against non-degenerate companions and further supports
a near-Chandrasekhar-mass explosion origin. Off-center ignited
delayed-detonations of Chandrasekhar-mass white dwarfs may be responsible for
the observed features of SN 2021aefx in some normal Type Ia SNe.
