Anime

Chouun is a mysterious girl who appears calm, collected, and very powerful. She is the second person to join the group. She loves to tease Kan'u and other women frequently. She also assumes the identity of a hero of justice named Butterfly Mask, hence wearing a Butterfly mask.

In Shin Koihime Musou, Chouun (in Kachou Kamen's form), saves Ryuubi from bandits with her secret technique, making Ryuubi develop a crush on Kachou Kamen. Chouun asked Ryūbi who saved her, and she "innocently" said good things about her (Kachou Kamen is super cool, and noble), raising Chouun's mood high. Chouun is also scary when she's smiling (Sui will have nightmares about it and Shion won't let her daughter sees Chouun's smiling face). Chouun even continues teasing Kan'u in more ridiculous ways (like an embarrassing introduction of Kan'u to the bandits who attacked Ryuubi—and Chouun gets a lump on the head as a result).

In Koihime Musou's OVA, Chouun (as Kachou Kamen) appeared and swam, but Kouchuu, who acted as the school's doctor, said that its okay, since Kachou kamen's appearance looks like Chouun, and she immediately tied up and put into an unused class, until night and no one seems to notice her missing (even her daughter, who asked about her whereabouts before).

Visual novel

When Kan'u was fighting the Tou army, she fought alongside Chouun for a while; when this war ended, Chouun met Kazuto and took a liking to him, promising to join his army later. She joins alongside Kouchuu after the battle with Enshou. She has a strong obsession of menma. She also has a habit of running around the city as the masked hero of justice "Butterfly Mask". Strangely, no one other than Kazuto and Shuri can recognize her true identity, despite only wearing a mask.

(Source: Wikipedia)