The younger sister of the Kakōton and also Sōsō's cousin and a general of Gi. She is first introduced taking part in the anti-Tōtaku campaign. During the war against Hongō faction she and her sister surrender and plead to Kazuto for aid after realizing Sōsō is being controlled. After Sōsō's rescue she becomes a captive of Hongō faction. She shows no signs of resentment towards Kazuto after being captured and even go as far as placing him as her 5th favorite later on (first three are Sōsō, her sister, and Kyocho. It's hinted that the fourth is Ganryō, which she neither confirms nor denies). Other than Sōsō, she's the only one capable of calming her sister.
She accepts Kazuto fairly early on in the story, and quickly becomes friends with him. She often gives him advice to help him adjust to his new life and even helps him out when he's caught in a difficult situation.
Despite being the younger one, she serves as a foil to her hot-headed sister. Always calm and collected, Kakōen rarely loses her cool, which plays a big part when keeping Kakōton in check. On the battlefield her sound judgement is often the only thing that prevents Kakōton from charging the enemy at first sight. Although she is no match for an actual strategist, she is still very intelligent and could fill in as a strategist in a pinch. Like Sōsō, she was also able to (partially) understand Kazuto's situation. In everyday life she is very nice and easy to get along with, but occasionally she likes to tease Kakōton and Kazuto in her own subtle way (or teaming up with Kazuto to tease her sister). Furthermore, she does enjoy being pampered, and should the opportunity arise, will act accordingly to get the attention she wants. Due to her levelheaded nature, she does not stand out much compared to many of the other girls.
In the anime her personality is greatly reduced (largely due to the improvement of Kakōton as a character), making her a lackluster minor character. Her calmness remains, but her intelligence and the rest of her charm are largely shadowed.
Like her sister, Kakōen is in a lesbian relationship with Sōsō. However, she doesn't share the same extreme devotion and does not harbor any negative feelings towards men. As a result, she easily develops a normal romantic relationship with Kazuto. She also doesn't mind sharing him with her sister and Sōsō.
In the first VN it is implied that she has some form of an incestuous relation with Kakōton, although to what extent is unknown. In the second VN she is blatantly a siscon, she finds Kakōton's slow-wittedness cute and will even resort to stalking just to observe the latter's "cute" behavior.