Tōma launched the manga in Shogakukan's Cheese! magazine in January 2019. The manga is set in the world of Tōma's earlier Dawn of the Arcana manga. Shogakukan published the manga's 16th volume on August 24.
Viz Media is releasing the manga in English and it describes the story:
In this kingdom, Ajin are considered no better than beasts. The men are sent to war, the women serve in brothels. Those who are lucky enough to live to old age spend their last years doing degrading, menial work. Boys who show signs of magical ability must serve the imperial family in the palace. Rangetsu's twin brother is sent to the palace to serve the Prince Tenyou, but he only lasts a short time before he is murdered. Rumors say his master was the one who aimed the blade, and Rangetsu decides to puts aside her femaleness in order seek revenge. After years of excelling on the battlefield, she has finally found her way to Prince Tenyou's side. But he isn't what she expected, and the webs of intrigue in the palace is more tangled and venomous than she imagined. Can Rangetsu find her vengeance before she too falls prey to palace plots, and will her inconvenient feelings for the Prince Tenyou be a hindrance or a help?
Tōma's Dawn of the Arcana manga launched in Cheese! in 2009, and ended its run in 2013. Shogakukan published 13 compiled book volumes for the manga. Viz Media has published the manga in English.
Tōma launched The Water Dragon's Bride (Suijin no Hanayome) manga in Cheese! in February 2015, and ended it in September 2018. Shogakukan published the manga's 11th and final compiled book volume in January 2019. Viz Media has also published the manga in English.
Source: Rei Tōma's X/Twitter account