Chachamaru

Chachamaru is a feline familiar that assists in Tamayo's medical research with Demon blood.

Appearance
Chachamaru is a small, tricolor calico cat with black, white and brown spots. It has big amber eyes. On its back, it wears a brown box with a syringe created by Tamayo with the purpose of collecting demons' blood. Around its neck, it wears a necklace with a paper talisman that was made and given by Yushiro, which it uses to hide with Yushiro´s Blood Demon Art.

History
No information is given on the cat, it is simply introduced as Tamayo's familiar used as a transport mechanism for her medical studies. It can be presumed that it has been helping Tamayo and Yushiro for quite some time, as it is well-trained. Like many cats, Chachamaru likes pets, and will briefly stop for them before returning to its work.

Yushiro decided to demonize Chachamaru before the historical battle against Muzan, however no specific details are given regarding the process of its transformation.

Drum House Arc
Chachamaru first appears after Tanjiro's battle with Kyogai, initially it arrives invisibly until it meows and is revealed to Tanjiro. Once the blood is tucked into the box on its back, Chachamaru hops away and becomes invisible once again to avoid detection.

Entertainment District Arc
After Tanjiro's battle with Gyutaro and Daki, Chachamaru appears swiftly to collect the blood from Tanjiro. It is given a small pat by Tanjiro before it hops away and returns to Tamayo.

Swordsmith Village Arc
Although Chachamaru doesn't collect any blood during the battle against Gyokko and Hantengu, it is seen delivering a note written by Tamayo, seemingly to inform Tanjiro that there is a possibility that Nezuko is capable of overcoming the sunlight.

Dimensional Infinity Fortress Arc
Chachamaru is seen during the battle with Muzan, after the Infinity Fortress collapses. The cat jumps above the remaining pillars in order to administer an antidote to stave off the poisonous effects of Muzan's attacks. As a result, it is sliced in half by the demon.

Abilities and Powers

 * As a feline, it did not posses any magical powers. However, it was able to disappear due to a spell of invisibility cast on it by Yushiro, it would activate this spell by meowing whenever it arrived to collect blood.
 * After it became demonized, Chachamaru possessed the ability to withstand beheading as seen when Yushiro was able to put it back together after it was dismembered by Muzan.

Trivia

 * They seem to like Tamayo, but find Yushiro annoying.