Fus-e's Links
Soul's dearest friend and and trusted mount. The two are usually never apart and are always seen traveling together. Ruth is ferociously protective of Soul to the point where if something goes near her he'd attack them when given the chance and will proceed to demonstrate how he got got his name.
The only one passive of this is Soul's older sibling, Renshu.
Soul puts her life in Ruth's claws more often then he does her. He controls her when she's unusually reckless or feeling hopeless in situations she can't bear alone, thus making him a lifeline.
The two are always with each other, one reading the maps and the other taking the steps, and are rarely ever seen apart. Ruth says he's known Soul for a lifetime, but that's yet to be explained thoroughly.