As part of our fine art training at Korinji we practice calligraphy of bonji, or Sanskrit characters (also called siddham). Unlike Chinese characters, these are often drawn with a flat wooden stylus rather than a brush.
Bonji are especially important in esoteric Buddhist practice. The characters are mantric seed syllables of various buddhas, bodhisattvas, and deities, but are not simply letters indicating sounds: they are seen as actual manifestations of those beings.
Bonji are used on protective amulets created by Zen priests, for example Korinji's omamori. Visualizing bonji is an important part of practices found in the Shingon, Tendai, and Shugendo traditions (including the Shugendo training done at Korinji).