This path is assigned the tarot trump Death, and the pairing is direct: Death, the card not of literal ending but of transformation, of the clearing-away that makes renewal possible, answers to its zodiacal sign Scorpio, the sign of death and rebirth, and to the letter Nun, the fish of the deep waters from which life is renewed. The Golden Dawn read the card as the necessary dissolution that precedes regeneration, in keeping with the Scorpionic mysteries. The correspondence of letters to tarot trumps was proposed by Eliphas Levi and codified by the Golden Dawn from 1888, in the scheme given in Liber 777.
The layers must be distinguished. The path from Tiphareth to Netzach, the letter Nun, and its attribution to Scorpio are Jewish in origin, from the Sefer Yetzirah, whereas the identification with Death is Hermetic Qabalah, the Victorian Western magical overlay, a construction of 1888 that has no standing in the Jewish Kabbalah from which the path and letter derive.