Ghost of Undecimber

• Ja Kanji — 13月のゆうれい • Ja Romaji — Jūsan Gatsu no Yūrei

• Type — manga • Author — Suzume Takano • Publisher — Shodensha • Imprint — Feel Comics Swing • Magazine — Feel Young • First — January 8, 2015 • Last — December 8, 2016 • Volumes — 2 Ghost of Undecimber, known in Japan as "The Ghost of the Thirteenth Month", is a Japanese manga series created by Suzume Takano. Shodensha serialized it in their josei manga magazine Feel Young from January 8, 2015, to December 8, 2016, and released it across two collected tankōbon volumes in 2016–2017. The story follows a love triangle involving Neri, a woman who dislikes being feminine; Kiri, a cross-dressing man; and Suō, an otherwise heterosexual man who finds Kiri attractive. The series was critically well received for its themes of questioning gender roles, and was selected as one of the recommended works at the Japan Media Arts Festival in 2018.

Ghost of Undecimber follows Neri, a woman who dislikes cute things and is uncomfortable with being feminine; Kiri, her twin brother who only feels at ease when cross-dressing in cute and feminine outfits; and Suō, Kiri's roommate. A love triangle develops as Neri becomes attracted to Suō, who in turn finds Kiri attractive when wearing women's clothes, despite otherwise not being attracted to men.

Ghost of Undecimber was written and drawn by Suzume Takano, and was serialized irregularly by Shodensha in their josei manga magazine Feel Young from January 8, 2015, until December 8, 2016. They have also released it in two collected tankōbon volumes in 2016–2017 under their imprint Feel Comics Swing, which include an additional chapter each that was not part of the magazine serialization. Takano struggled with the schedule of the serialization, submitting each chapter to the publisher close to the deadline, and then went back to touch up the art for the release of the collected editions; the final chapter was particularly difficult, as one of Takano's family members died while she was in the middle of producing it.