What is Ubu Nakago in Japanese Katana terminology?

The term "Ubu Nakago" (生ぶ茎, うぶなかご) refers to the tang of a Japanese sword that has been preserved in its original state, without undergoing any processes such as "Suriage" (磨上げ) or "Machiokuri" (区送り). This term is used to describe a sword that has maintained its original form since the time it was created, without any modifications or alterations made in later generations. This is significant in the study and appreciation of Japanese swords, as it provides valuable insights into the swordsmith's original intentions and techniques. The preservation of the original state of the tang also contributes to the historical and cultural value of the sword.