Solution
= Solution
Here $i^3=-i$, so the <argument> condition concerns $z+i$. Writing $z=x+iy$, the <complex number> $x+i(y+1)$ must point along the direction $1+i$. Consequently
$$
\boxed{z=-i+s(1+i),\quad s>0,\qquad\text{equivalently }y=x-1,\ x>0.}
$$
This is an <open ray> in the <Argand plane>, rather than the whole straight <line>. Its endpoint $z=-i$ is excluded because the <argument> of zero is undefined; the opposite half-line has a different <argument>.