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In the pursuit of enhanced engine performance and reduced emissions, the design of liquid-fueled propulsion systems is shifting towards much higher combustor pressures, surpassing the nominal critical pressure of the fuel and air. This trend leads to the adoption of supercritical conditions, wherein the liquid fuel is injected into the ambient air at supercritical pressure and temperature, causing the fuel temperature to exceed its nominal critical point. This transition from a liquid-like to a gas-like behavior, known as "transcritical behavior," is a crucial aspect governing the operation of modern high-pressure propulsion and energy conversion systems. In these systems, the primary liquid jet breakup and the subsequent break-up of the resulting droplets into smaller droplets, namely secondary breakup, significantly impact mixing and combustion processes. Despite its importance, there has been a limited focus on droplet breakup at supercritical conditions, particularly at higher flow speeds relevant to high-speed liquid-fuel propulsion systems. Surface tension effects are often neglected in the simulation of transcritical flow, assuming surface tension vanishes beyond the critical point, while recent experiments and molecular dynamics simulations suggest that surface tension effects persist at transcritical conditions. To gain insight into the effects of surface tension on transcritical flows, we have developed a fully compressible multiphaseDirect Numerical Simulation (DNS) approach that accounts for decaying surface effects. The diffuse interface method is employed to represent transcritical interfaces, accounting for surface tension effects calculated using molecular dynamics simulations. This approach is employed to investigate the behavior of subcritical n-dodecane droplets in a supercritical nitrogen environment interacting with a shockwave, aiming to identify the governing breakup regimes at transcritical conditions. The development of quantitative measures enables the generalization of droplet breakup modes for transcritical droplets. The insights gained from this study contribute to advancing the understanding of transcritical liquid breakup, providing valuable knowledge for designing and optimizing high-speed propulsion systems