Massive galaxies are unique probes of both cosmology and galaxy evolution. They highlight the fabric of our universe and help us trace massive dark matter halos through cosmic history. In recent years, two new developments significantly advance our understanding of these massive galaxies. 1) The increasingly deeper images map their stellar mass distribution to the extreme outskirt. 2) The unprecedented galaxy-galaxy lensing capability is renewing our understanding of their dark matter halos with direct measurements. Using data from the Hyper Suprime-Cam (HSC) survey, I will demonstrate that the combination of these two approaches reveals an intriguing relation between the structure of massive galaxies and halo assembly history. This relation can serve as the foundation of a next-stage galaxy-halo connection model. We build a preliminary model of such kind - ASAP - to demonstrate that it establishes a tighter connection between the central galaxy and its halo mass than the traditional stellar-halo mass relation (SHMR). It also helps us overcome systematic difficulties encountered by the galaxy richness-based optical halo-finder and form unbiased tracers of massive halos. I will discuss its potential on providing better characterizations of assembly bias and splashback radius as well as on improving the robustness of cluster cosmology.
