In the Heart of Kunoichi Tsubaki (Japanese: くノ一ツバキの胸の内, Hepburn: Kunoichi Tsubaki no Mune no Uchi) is a Japanese manga series written and illustrated by Sōichirō Yamamoto. It was serialized in Shogakukan's shōnen manga magazine Monthly Shōnen Sunday from January 2018 to May 2023, with its chapters collected in nine tankōbon volumes. An anime television series adaptation produced by CloverWorks aired from April to July 2022.
 Tsubaki, a kunoichi and the best student of the Akane Class, lives in a village where women are not allowed to have contact with men. However, she has a curiosity about them that she wants to keep hidden.
 Written and illustrated by Sōichirō Yamamoto, In the Heart of Kunoichi Tsubaki was serialized in Shogakukan's shōnen manga magazine Monthly Shōnen Sunday from January 12, 2018, to May 12, 2023. Shogakukan collected its chapters in nine tankōbon volumes, released from July 12, 2018, to August 9, 2023.
 On November 9, 2021, Aniplex announced an anime television series adaptation produced by CloverWorks. The series was directed by Takuhiro Kodachi, with the scripts handled by Konomi Shugo, character designs by Yousuke Okuda, and music composition by Yūsuke Shirato. It aired from April 10 to July 3, 2022, on Tokyo MX and other networks. The opening theme song is "Highlight - Highlight" (ハイライト・ハイライト, Hairaito Hairaito) by the Peggies. For each episode, different cast members performed a version of the ending theme song "Akane-gumi Katsudou Nisshi" (あかね組活動日誌) as their respective teams. Crunchyroll has licensed the series. Medialink has licensed the series in Asia-Pacific.
 Team Dog is pitted against Benisumomo, Mizubashou, and Touwata of Team Sheep in combat training. Touwata asks Tsubaki to beat Benisumomo to teach her a lesson about her laziness. As the combat begins, Sazanka and Asagao capture Touwata but are captured by Mizubashou. Tsubaki, who knows Benisumomo trains in secret to maintain her reputation as a prodigy, duels her to a draw. Touwata promises that one day, she will become stronger than Benisumomo and prove that hard work is superior to natural talent.
 Team Dog is assigned to collect food, but Sazanka and Asagao constantly bicker. The twins Kikyou and Uikyou of Team Snake challenge Team Dog to steal a scroll from them. To make them work together, Tsubaki ties Sazanka and Asagao together and refuses to help. Once they finally catch up with the twins, the latter uses a sleep Jutsu on them. Sazanka and Asagao counter this by pinching each other and trap the twins before falling asleep. Afterwards, Tsubaki realizes the scroll was blank, but is happy that the two worked together.
 Konoha captures Tsubaki with a dancing leaves and sleep Jutsu. When she wakes up, Hana and Konoha explain that their village used to be integrated, but the men and women kept falling in love, eloping, and leaving the village. To stop this, their leaders separated and told the lie about the opposite gender being dangerous. Tsubaki agrees to keep the secret in exchange for the students getting supper. After hearing Hana describe what love is, a confused Tsubaki realizes she is feeling it.
 Asagao leads Team Dog to her secret grove of fruit trees, but finds Hinagiku, Kibushi, and Oniyuri of Team Horse eating the fruit even though she wrote her name on them. After an argument, they decide to settle the matter with a cuteness contest between Tsubaki and Hinagiku. Team Horse cheats by hypnotizing Asagao and Sazanka into voting for Hinagiku. Tsubaki counters by duplicating herself, but is so nervous that her duplicates fade before they can vote. However, Tsubaki's nervous face is so cute that Hinagiku forfeits and gives up the fruit.
 The class gets a new transfer student. The student, who wears a mask due to her shyness, is rescued by Tsubaki after she referred to herself using a male pronoun. She introduces herself as Rindou and confides that she was raised as a boy. After briefly seeing her without her mask, Tsubaki asks Rindou to remove it to prove she is a girl, but she refuses and instead drops her pants to prove she does not have a "ding-a-ling". Once the other students are convinced about the situation, Tsubaki becomes embarrassed.
 Rindou tries to practice removing her mask in public, but is too shy. Sazanka tries to remove it and is scolded by Tsubaki. As Sazanka complains that she just wanted to see her cute face, Team Horse overhears and Hinagiku wants to see for herself, so she asks Sazanka and Asagao for help. They lure Rindou into a trap, but Sazanka and Asagao turn on Team Horse and Rindou was really Tsubaki in disguise. Rindou decides to remove her mask permanently, dazzling Hinagiku.
 Dokudami, Aogiri, and Shakuyaku of Team Boar return from a long journey and share boar meat with the others. Team Dog explains to Rindou that Team Boar are the village's strongest warriors. Asagao tries to compliment them by calling them "stupid strong", but they think she was calling them stupid and attack her. Tsubaki challenges Dokudami to a duel and she accepts after greeting the teachers. Team Dog relaxes and explains Team Boar always gets lost. Mokuren confirms Team Boar cannot find the battlefield and walked into a swamp.
 Hana promises to treat anyone who can catch her pet snakes to dinner. Tsubaki catches one, but lets Team Tiger have it. As they search for more, Tsubaki is irritated when Sazanka and Asagao jokingly call the snakes men and lectures them. While Tsubaki helps repair Rindou's mask strap, Rindou teaches her the differences between men and women, but when she mentions the "ding-a-ling" resembles a snake, Tsubaki is so shocked that she lets a snake go past her and Ajisai catches it.
 Tachiaoi of Team Rat doubts herself because she can never say "No" to her teammates Higuruma and Hagi. As Higuruma drags them on a boar hunt, Tachiaoi witnesses Tsubaki disciplining her team. Inspired, she tells Higuruma and Hagi to practice throwing shuriken, but they did not bring any, so they practice fire Jutsu. It rains and they take shelter in a cave. Tachiaoi laments her inadequacies as a leader, but her teammates reassure her. When the rain stops, they bathe in a hot spring and Tachiaoi vows to find her own path.
 During a concert put on by Team Rabbit, Rindou says they are attractive. After explaining to Team Dog what that word means, they interpret it as tricking a man into dropping his guard and ask her to teach them an attractiveness Jutsu. She teaches them to make sexy poses. Sazanka and Asagao quickly master it, but Tsubaki's attempt just makes them laugh and say she looks ridiculous, making her cry.
 Ajisai and Ume keep making Hinagiku cry by taunting her with the attractiveness Jutsu. While Oniyuri chases them, Kibushi asks Benisumomo to cheer Hinagiku up. Instead, Benisumomo repeatedly taunts her. Benisumomo realizes she took her joke too far, but Hinagiku cheers up, thinking Benisumomo sees her as a rival. When Oniyuri arrives with Ajisai and Ume, they see Benisumomo taunting Hinagiku again.
 In 2020, the manga was one of the 50 nominees for the sixth Next Manga Awards. 
 The anime adaptation was one of the 100 nominees for the Anime Fan Award during the 2023 Tokyo Anime Award Festival, placing fourth behind Tiger & Bunny 2, Uta no Prince-sama: Maji Love 1000%, and Mechamato.
 Anime News Network reviewers Caitlin Moore, Richard Eisenbeis, Nicholas Dupree, James Beckett, and Rebecca Silverman greatly criticized the premise, calling it "contrived, uncreative, and unfunny". While some praise was given to its art style, the series was also criticized for its "questionable artistic decisions", referring to the character designs and outfit choices.