Slug

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

Offensively, slugs can shoot acid from their mouths. Defensively, slugs can divide themselves into many smaller replicas. The slugs can encapsulate an individual's entire body, making use of their extreme durability to protect the person inside from physical harm or in stasis to prevent loss of life.

Katsuyu can also absorb chakra from its summoner and even control it to some extent, as shown through the use of the Katsuyu: Immense Network Healing technique where the summoner can channel their chakra to Katsuyu in order to heal persons over a wide range without physically being there. Through this technique the summoner also shares a sensory link with Katsuyu and can gather a basic understanding of a persons physical status amongst other things making slugs also an excellent source for information gathering.

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 Naruto chapters 4, 153, and 162.