Leather, Rubber and Enamel aka. "The Bondage Sisters" are the three main antagonists of the ero adventure manga "Dragon Pink Volume 3: The Last Fight" (ドラゴンピンク THE LAST FIGHT) by creator Itoyoko.
The trio invade the castle of Princess Delta Pubic III in order to kill Pink (one of the main protagonists) as she is prophesized to contain the power to purify the evil "Yin Monsters", which the Bondage Sisters are a part of. The lead sister, Leather, first attack's the castle guards by summoning her "Beast Knights" and then follows up with her "Beast Bomba". Rubber and Enamel soon join in and use "Bondage Cross" and "Bondage Storm" to clean up the remaining soldiers. The assault quickly draws the attention of Pink, her master, Santa, Princess Delta and her servant, Maze. When Leather uses her "Beast Armor" attack, Maze sacrifices herself to save her princess. The splattered blood from the attack manages to release a curse from Delta, which unlocks her true powers.
Now more than a match for her antagonists, Delta effortlessly slices through the Bondage Sisters, giving Santa an opportunity to kill both Enamel and Rubber with his sword. As a last ditch move, Leather transforms herself into a giant monster, but it is all for naught as Delta's shadow power slaughters her by cutting all the way through her abdomen.
Chibi Leather, from the book cover.
Chibi Enamel, from the book cover.