We study a time-fractional superdiffusion equation involving a \(\upvarphi \) -Caputo derivative and a fractional Laplacian within a Lorentz-space framework. First, we analyze the associated linear problem. By combining the Fourier transform in space with the \(\upvarphi \) -Laplace transform in time, we derive explicit representation formulas for the Green kernels. These kernels are expressed in terms of Fox \(H\) -functions, which allow us to obtain sharp pointwise bounds and decay estimates in Lorentz spaces. We then consider the corresponding semilinear equation with a singular source term. Using the linear estimates, we establish local well-posedness of mild solutions in weighted Lorentz spaces, together with continuous dependence on the initial data and a blow-up alternative. Finally, we discuss the scaling structure induced by the decay estimates and identify \( p_c(\uprho )=1+\frac{2\updelta \,\uprho }{\upalpha d} \) as a natural candidate critical exponent in this setting.