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 a white base accompanied by black 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 feline 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.

In preparation for the final battle, Tamayo managed to transform Chachamaru into a demon, an act that weighed heavily on her heart. Despite Chachamaru having no agency or decision in the matter, Tamayo's primary concern was ensuring that Yushiro would not be left in solitude and consumed by loneliness. Interestingly, Chachamaru's own sentiments revealed a content acceptance of the transformation, driven by its unwavering love for Tamayo. No specific details are given regarding the process of its transformation.

Tsuzumi Mansion Arc
Chachamaru first appears after Tanjiro's battle with former Lower Moon Six 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 Upper Moon Six 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 after the battle against Upper Moon Four Gyokko and Upper Moon Five Hantengu, it is seen delivering a note written by Tamayo, seemingly to inform Tanjiro that there is a possibility that Nezuko Kamado is capable of overcoming the sunlight.

Infinity Castle Arc
Chachamaru is seen during the battle with Muzan, after the Infinity Castle collapses. The cat jumps above the remaining Hashira in order to administer an antidote to stave off the poisonous effects of Muzan's attacks. As a result, it is sliced in pieces by the demon and lay struggling on the ground for a while. Some time later, Yushiro found the cat and reassembled it. The Demon Slayers accompanying Yushiro, Murata and Takeuchi, reacted in surprise when they saw it and Yushiro explains that they turned it into a demon right before the battle.

Abilities

 * 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 a demon, 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

 * Chachamaru seems to like Tamayo, but it finds Yushiro annoying.
 * The kanji in Chachamaru's name means "tea" (茶) and "circle, round" (丸), with 々 being an iteration mark.
 * Chachamaru's gender is presumably male, as it is described to be the manliest cat ever, and listed as male in the Missing Cat poster in Kimetsu Academy.
 * This would be an unusual case, as calico cats are biologically predominantly female, except under rare genetic conditions.
 * Chachamaru is one of, if not the only, demons that was never human to begin with.
 * In Kimetsu Academy, Chachamaru is Yushiro's family's cat, which he once brought to school on a whim. The cat took a liking on Health Teacher Tamayo and has since then started following him to school. Because they couldn't keep it contained in the school's infirmary, they let her out, after which the cat is found by Civics teacher Gyomei Himejima, who thought the cat was lost.

Navigation
Чачамару 茶々丸 茶茶丸