dark
眛 centers on darkness, especially dimness or obscurity of sight. The single given meaning 'dark' captures a state of being poorly lit or hard to see.
眛 combines 目 (eye) with 未, which likely contributes the sound and may suggest something not yet clear or visible, giving the idea of dim or dark sight.
The eye 目 beside 未 (not yet) suggests vision that hasn't yet become clear: everything is dark and hard to see.
For マイ, imagine your eyes struggling in the dark, and you say 'my eyes can't see': my -> マイ, tied to the dim vision of 眛.