This is Rachel's tattoo.
"Walk without rhythm" is a reference to Dune by Frank Herbert.
On the desert planet Arrakis any type of rhythmic vibration in the deep desert will attract an immense sandworm which will destroy ie engulf anything it finds (person, spice mine, space ship) in an effort to protect its territory. The desert Fremen have developed a way to walk without any discernible rhythm, only calling the sandworms to them with 'thumpers' when they choose.
Dune is my favorite novel, hence the desire for a Dune tattoo, but choosing a quotation was too hard so I referenced the Fremen, who play a central role in the story arc.
This is John's tattoo.
I must not fear. Fear is the mind-killer. Fear is the little-death that brings total obliteration. I will face my fear. I will permit it to pass over me and through me. And when it has gone past I will turn the inner eye to see its path. Where the fear has gone there will be nothing. Only I will remain.
- From Dune by Frank Herbert