Navkar mantra has 68 akshar (letters) in the traditional counting. The 54th akshar falls in the later part (the Chulika). In that sequence, the 54th letter corresponds to the guru-letter “vve” (spoken as vva/vve in some recitations). This is one of the letters classified as a guru in the Chulika section.

You can read more about how the Navkar mantra is counted and its akshar distribution here