Katsuyu is a giant slug and the personal summon of Tsunade, the Fifth Hokage, in the Naruto series. Known for her calm and gentle personality, Katsuyu plays a supportive role in battles, providing healing abilities and acting as a messenger. Her unique ability to split into smaller slugs allows her to cover large areas, offering protection and support to allies. Unlike other summons, Katsuyu is not aggressive and focuses on healing and support, highlighting her importance in the medical ninja domain.