seiji's twin fraternal sister
has a bad habit of trying to steal her brother's attention away from any girl her brother might be dating or with at the time
has a brother complex

carries around a large sword but smaller then seiji's but was taught swordsmanship by her brother

She was born 30 minutes after seiji making her the youngest of the two.

she only has eyes for her brother but can have moments of bi curiousness
she has an almost identical scar to her brothers but her's is smaller and was self inflicted* wanting to be like her big brother when she was a bit younger. (its a mark seiji looks at in shame due to not being the protective brother he should have been )

*I DON'T CONDONE SELF HARM IN ANY WAY
ITS ONLY PART OF THIS STORY ONLY TO SHOW HOW CRAZY OBSESSED KOTO IS ABOUT HER BROTHER.