At junctions between plate boundaries there are several general characteristic features. These include trench-normal fast polarization direction of S-wave splitting in the mantle wedge, along-arc variation of the angle of subduction, and the different behavior of slab stagnation along the strike of the trench. In this paper, we focus on the junction of the Tohoku–Kurile arc. We show the dynamical effects of the junction using a numerical model of mantle convection with a realistic curved shape of the trench. We obtain 3D flow in the mantle wedge which is consistent with the observation of seismic anisotropy even with the oblique subduction. We also find the along-arc variation of subduction angle which agrees with the observations, although the match becomes worse when we include the effect of dislocation creep, that is, non-linear viscosity. Along-arc variation of the angle of subduction partly contributes to the different behavior of slab stagnation in the Tohoku–Kurile arc. Our results show that the shape of the trench is an important factor which considerably affects mantle flow and deformation of subducting slabs. Thus, 3D modeling is necessary to constrain the dynamics of subduction zones near the junction.