gap moe; attraction to a gap between appearance and true nature
Slang from otaku culture; describes finding someone endearing when their behavior or personality unexpectedly contrasts with their outward image (e.g., a tough-looking person being gentle).
My usually cool senior was talking gently to a kitten, and I felt gap moe.
Her gap moe point is that she looks serious but actually has a sweet tooth.
Compound of ギャップ (gap, from English) and 萌え (moe, a slang term for budding affection). The exact origin is uncertain, but it emerged in otaku and internet communities.