there's a fork that adds proper tategaki support - https://github.com/m-tky/koreader-tategumi https://github.com/m-tky/koreader-tategumi and with the plugin sy

there's a fork that adds proper tategaki support - https://github.com/m-tky/koreader-tategumi https://github.com/m-tky/koreader-tategumi and with the plugin system allows you to use the built-in Japanese dictionary a la Yomitan with one-tap lookups