A note on Horimono;
The Drifting Cloud, known as Ukigumo (浮雲) in Japanese can be seen ascending the blade. Clouds are Buddhist representations and can be found in many works of art and narrative. In Buddhism, clouds signify the ‘Western Paradise’ beyond earth; and in Shintoism, the spirits of the dead.

Soure: https://nihontoantiques.com/project/katana-sword-fss-725/