She is Convinced that her Half-Brother is a Girl (Black & White)

片親の違う弟を妹だと思い込む姉 kataoya no chigau otouto o imouto dato omoikomu ane

Narumi-kun's sister is convinced that he is a girl. No matter how many time he tells her. This is a remake as a 4-koma of the original colored webcomic.

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