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The Tokyo metropolitan area, in the Kanto region of Japan, lies on the Okhotsk plate. Historically, the city has suffered severe damage as a result of megathrust ruptures and intra‐plate earthquakes (M≥ 7) caused by the dual subduction of the Philippine Sea (PHS) slab and the Pacific slab. To understand the unique seismotectonics of the region, we constrain the three‐dimensional (3‐D) Pwave isotropic and azimuthal anisotropic velocity structure beneath the Kanto district, by applying a high‐resolution anisotropic tomography method to travel time data from a dense seismic network consisting of ∼500 stations (including the Metropolitan Seismic Observation network, MeSO‐net). The seismic structure, derived from 1,877 local earthquakes, suggests that the basement of the Okhotsk plate consists of an old accretionary zone formed when the NE Japan arc was part of the Asian continent. The anisotropy observed in the oceanic crust of the subducting PHS slab suggests the presence of a well‐developed system of bending‐related faults, oriented parallel to the axis of the Sagami Trough. We identify a low‐velocity anomaly within the PHS slab mantle, located beneath the Boso Peninsula, which has previously been interpreted as representing the overlying continental plate or the oceanic crust of the PHS slab. Lateral variations in the anisotropy structure suggest that the NE limit of the PHS slab lies farther south than previously thought. Anisotropy directions can be used to identify heterogeneities embedded in low‐velocity anomalies within the PHS slab, which have not been identified in previous studies using only isotropic velocity models. The Tokyo metropolitan area has been severely damaged by M7‐ and M8‐class earthquakes caused by the interaction between the Philippine Sea (PHS), Pacific, and Okhotsk plates. To understand the seismic activity and subsurface structure in the region, we analyzed seismic data from the Metropolitan Seismic Observation Network (MeSO‐net). We focused our investigations on characterizing the 3‐D structure of seismic anisotropy, which has a close relationship with the stress field and deformation beneath the Tokyo metropolitan area. We produced high‐resolution 3‐D tomography images of the Pwave isotropic and azimuthal anisotropic velocity structure beneath Kanto, Japan. The main results are as follows. (1) The PHS slab surface is shallower than inferred in previous isotropic velocity studies. (2) The NE limit of the PHS slab can be south of the position inferred previously. (3) The existence of bending related faults within the subducting PHS slab crust and oriented parallel to the axis of the Sagami Trough is consistent with the anisotropy patterns. This is the first tomography study to analyze data from the dense MeSO‐net network. First report of seismic tomography analysis using travel time data retrieved by the Metropolitan Seismic Observation network seismic networkAnisotropy structure constrains the geometry and setting of the subducting Philippine Sea slab, revealing it is shallower than thoughtThe northeastern limit (leading edge) of the Philippine Sea slab can be south of the position suggested previously First report of seismic tomography analysis using travel time data retrieved by the Metropolitan Seismic Observation network seismic network Anisotropy structure constrains the geometry and setting of the subducting Philippine Sea slab, revealing it is shallower than thought The northeastern limit (leading edge) of the Philippine Sea slab can be south of the position suggested previously