\begin{scope}[node distance=0.75cm]

\node (KGX)
  [xshift=-0.55cm, inner xsep=0.01cm, inner ysep=0.03cm]
  at (0, 0) {@};

\node (K)
  [xshift=0.25cm, inner xsep=0.01cm, inner ysep=0.03cm, below of=KGX, left of=KGX]
  {K};

\node (GX)
  [xshift=-0.45cm, inner xsep=0.01cm, inner ysep=0.03cm, below of=KGX, right of=KGX]
  {@};

\node (G)
  [xshift=0.45cm, inner xsep=0.01cm, inner ysep=0.03cm, below of=GX, left of=GX]
  {g};

\node (X)
  [xshift=-0.45cm, inner xsep=0.01cm, inner ysep=0.03cm, below of=GX, right of=GX]
  {x};

\draw[->] (KGX) to (K);
\draw[->] (KGX) to (GX);

\draw[->] (GX) to (G);
\draw[->] (GX) to (X);

\node (Stk0) [draw, shape=rectangle, minimum width=1.5cm, minimum height=0.75cm, anchor=center]
  at (-2.75, 0)     {};

\draw[->] (Stk0.center) to (KGX);

\end{scope}