Japan has one of the best stated and regulated waste management programs worldwide, befitting its shortage of disposal sites and sheltered resources. While being the 5th largest biomass market worldwide, its efficient waste management accounted for a biomass recycling ratio near 71 % in 2020. Still, Japan has a substantial capacity for bioenergy and carbon capture, as its supply chain remains mostly non-renewable-based. A biorefinery prospect is to foray into biochemical production integrated with bioenergy technologies. However, detailed insights are scarce in the literature for a thermochemical biorefinery to biochemicals in Japan. This study aims to clarify the more promising Japanese solid biowastes for thermochemical conversion into bioproducts and bioenergy. For this, technical and regulatory analysis was deployed to fit the interests of the Japanese administration. Conversion of biomass to biochemicals (light olefins and BTX) was calculated using overall rates in the literature. Forest residue (leftover/thinning), rice waste (straw/husk), and cardboard waste were the most available lignified biowaste in 2018. The work forecasted a theoretical substitution near 21 % of the Japanese petrochemical olefins or BTX produced in 2018. The current research precedes a more comprehensive study that deploys the simulation and optimization of thermochemical pathways, assessing the environmental impact and techno-economic feasibility.