  Previous X-ray spectral analysis has revealed an increasing number of AGNs
with high accretion rates where an outflow with a mildly relativistic velocity
originates from the inner accretion disk. Here we report the detection of a new
ultra-fast outflow (UFO) with a velocity of $v_{\rm
out}=0.319^{+0.005}_{-0.008}c$ in addition to a relativistic disk reflection
component in a poorly studied NLS1 WKK~4438, based on archival \nustar and
\suzaku observations. The spectra of both \suzaku and \nustar observations show
an Fe~\textsc{xxvi} absorption feature and the \suzaku data also show evidence
for an Ar~\textsc{xviii} with the same blueshift. A super-solar argon abundance
($Z^{\prime}_{\rm Ar}>6Z_{\odot}$) and a slight iron over-abundance
($Z^{\prime}_{\rm Fe}=2.6^{+1.9}_{-2.0}Z_{\odot}$) are found in our spectral
modelling. Based on Monte-Carlo simulations, the detection of the UFO is
estimated to be around at 3$\sigma$ significance. The fast wind most likely
arises from a radius of $\geq20r_g$ away from the central black hole. The disk
is accreting at a high Eddington ratio ($L_{\rm bol}=0.4-0.7L_{\rm Edd}$). The
mass outflow rate of the UFO is comparable with the disk mass inflow rate
($\dot M_{\rm out}>30\%\dot M_{\rm in}$), assuming a maximum covering factor.
The kinetic power of the wind might not be high enough to have influence in AGN
feedback ($\dot E_{\rm wind}/L_{\rm bol}\approx 3-5\%$) due to a relatively
small column density ($12^{+9}_{-4}\times10^{22}$~cm$^{-2}$). However note that
both the inferred velocity and the column density could be lower limits owing
to the low viewing angle ($i=23^{+3}_{-2}$$^{\circ}$).
