Slug

are the trademark summon of Contract::Tsunade - famed as - and her student, Contract::Sakura Haruno. The only known slug, Katsuyu, is summoned from the Shikkotsu Forest.

Offensively, slugs can shoot acid from their mouths. Defensively, slugs can divide themselves into many smaller replicas. The slugs or their replicas can encapsulate themselves around an individual's entire body, essentially making them a big cushion for the person inside, protecting the person from physical collisions. Katsuyu can also absorb chakra from its summoner and even control it to some extent, as shown when Tsunade transferred her own chakra to Katsuyu in order to heal the citizens of Konoha during Pain's Assault.

Trivia

 * The Six-Tails resembles a slug.
 * The acid-shooting powers are an exaggeration of real-life slugs' ability to regurgitate digestive acids in self-defence.
 * Although Katsuyu is the only slug that has been seen in the series, other slugs are shown on the cover pages of chapters 4, 153, and 162.