What is Kaen boshi in Japanese Katana terminology?

The term "火焔帽子" (Kaenboushi) refers to the name of the tempered edge of the tip (kissaki) of a Japanese sword. The term is derived from the appearance of the hardened edge (nie) of the sword flowing and tapering towards the tip, resembling a blazing flame. This type of tempering pattern can be seen in the works of "Yukimitsu" of the Soshu tradition and the Taima school, one of the five schools of Yamato, during the Koto period.