A Sarashi is a series of wrapped bandages worn across the chest of men or women for various purposes. Men wore them as undershirts and women as support for their breasts.
Usually tougher women wear their sarashi and expose it. For example, Aoi Kunieda and Aya Natsume show off their sarashi and skin. Also for men, especially the Yakuza and the samurai wear the sarashi because it makes them look tough while protecting them from certain injuries such as knife wounds.
Also, for endowed women, a sarashi is like a sports bra that helps to support the breasts and minimize back problems.
Other times, women wear sarashi to bind their breasts so they can disguise themselves as men. For example; a girl might pretend to be a boy in an all boy school to take up kendo. A famous cultural example would be Ryunnosuke who wears so she can fight with the boys and the sarashi helps maintains her tomboy personality.
Men can also wear sarashi especially samurais such as Samurai Jack or Sanosuke Sagara because a sarashi symbolizes toughness or manliness (Gar). For big men, a sarashi can also serve as a belt to help restrict big bellies.
Kamina is manly as he display his Gar with his sarashi that covers his rock hard abs plus he wears a pair of killer sunglasses.