The early universe had such an extremely high energy density that supermassive particles could have been produced. When heavy particles are pair produced during inflation via couplings to the inflaton, the particle mass generates a non-trivial curvature perturbation in position space. Even if the heavy particles no longer exist, the modified curvature perturbations are preserved before horizon re-entry and will generate locally-enhanced dark matter clumps or galaxy densities on the large-scale structure (LSS). We explore these signatures by studying the matter power spectrum and the abundance of massive halos, and discuss the discovery potential. We will go through the details of implementing the curvature perturbations in the N-body simulations with appropriately modifying initial conditions, and talk about several subtleties that we are currently coping with. It will allow us to properly include non-linear effects, and investigate a pairwise nature of signals which is difficult to study analytically. Finally, I will briefly introduce other interesting literatures that explore early universe models with using N-body simulations, and their general aspects.