Among the swordsmiths in Bizen no Kuni, those before the Ichimonji school, which was established in the early Kamakura period, are collectively called Ko-Bizen. Tomonari was a swordsmith who, together with Masatsune, represented the Ko-Bizen school and is said to have been active around the Eien era (987 to 989). This was the time when the wanto (curved) form with a ridgeline was completed as the form of Japanese swords. This tachi (swords made to be worn with the cutting edge down) is considered to be one of Tomonari's oldest swords and shows a refined antique shape: a slim blade with high koshizori (the deepest part of the curve close to the tang), funbari (a blade that tapers towards the tip) and kokissaki (short tip of the blade). The jigane (ground metal) features a wood grain pattern with some traces of rough forging (hadadatsu) and faint utsuri (a white misty formation) while the hamon (blade pattern) features komidareba (a small irregular pattern) with little difference in height, ashi (martensite crystals extending from the hamon to the cutting edge) and yo (a falling leaf-like activity in the hamon).