Thanks to the anisotropic radiation of elementary dipoles, greatly enhanced laser gain can be achieved by simply adding side-reflection planes for the radiating waves. To verify this fundamental physics concept, we exploit the strong z-polarized Raman response of KTiOPO4 by resonating off-axis Stokes waves in the x-y plane of the crystal with reflection feedback from the y-surfaces. When pumped by a laser pulse with a length comparable to the crystal length, such an anisotropic off-axis Raman oscillator generates a single off-axis mode with 30% optical efficiency. The anisotropic gain enhancement factor of this Raman laser is about 1.3x10(4) compared with one oscillating the Stokes polarization in the x-z plane.