A novel lightweight and high-accuracy variant of the image pan-sharpening technique is designed for Himawari-8 multispectral images. This method, named Additive Template Sharpening, injects higher-wavenumber components of the highest-resolution Band 3 images into lower-resolution visible or shortwave infrared images, thereby providing multispectral high-resolution images. This injection is realized by adding inter-band differential field to the high-resolution band, making use of the specific pixel arrangement of the Himawari-8 imager for simple and accurate coordinate transformations. Both subjective inspection of RGB composite images and objective evaluation of the upsampling indicate that Additive Template Sharpening exhibits higher accuracy than existing methods for Bands 1-6 of Himawari-8. This technique not only enables operational forecasters to diagnose atmospheric conditions in more details using higher-resolution RGB composites, but also provides higher-quality true-color imagery for the public.