Slugs (蛞蝓, Namekuji) are the trademark summon of Tsunade - famed as Konoha's Slug Princess Tsunade (木ノ葉のナメクジ綱手姫, Konoha no Namekuji Tsunade-hime) - and her student, Sakura Haruno. The only known slug is Katsuyu an enormous creature that is summoned — in parts — from the Shikkotsu Forest.^[1]

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 person's physical status amongst other things making slugs an excellent source for information gathering as well.

Trivia

• The Six-Tails resembles a slug and similarly possesses acid-based abilities. However, it is unknown if it has any connection to Katsuyu.
• 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.

References