younger sister
妹 centers on a female sibling who is younger: a younger sister.
妹 combines 女 (woman) with 未, which likely contributes the sound and the idea of something not yet fully grown, suggesting a younger female sibling.
A woman 女 who is not yet 未 fully grown: a younger sister.
For マイ, imagine your younger sister proudly showing you her new My Little Pony toy: My -> マイ, and she is your 妹.
younger sister
sisters
older brother and younger sister
cousin (female)
sister-in-law (spouse's younger sister or younger brother's wife)
cousin (younger female)
biological younger sister
younger brother and sister
foster sister
one's deceased younger sister
your younger sister
brother-sister inbreeding; sibling mating
quarrel between siblings
brothers and sisters; siblings
Bengalese finch; society finch (Lonchura striata var. domestica)
my love; my dear; darling
my love; my dear; darling
darling (woman); dear; honey; my betrothed
younger sister
young lady