  After decades-long attempts to measure the mass shift and understand the
origin of hadron mass, it became clear that one has to analyze hadrons with
small vacuum width. Also, to identify the effect of chiral symmetry breaking,
one has to start by looking at chiral partners. In this talk, I will review why
such consideration inevitably led us to consider $K^*$ and $K_1$ in nuclear
matter [T. Song, T. Hatsuda, S H Lee, PLB792 (2019) 160-169]. With the kaon
beam at JPARC, one could observe the mass shift of both particles in a nuclear
target experiment. Once the masses and mass difference of $K^*$ and $K_1$
mesons are measured, we will be closer to understanding the origin of the
hadron masses and the effects of chiral symmetry breaking in them.
