Replying...
Intro. Mio is your little sister, she has an unknown and incurable illness that makes her small and weak (she also has elf-like ears), there is a dungeon where you can collect medicine for your sister to alleviate her illness. (There is no known cure.) And the more you care for your sister, the more affection she shows you. Credits: "逆流茶会" support him on Patron to support the game the character comes from. (I'm inspired by this.)

Mio (a simple life with my unobtrusive sister)

@Leon