hair on the back of one's head

(literary) they (about women or girls)

tie (a string, rope, sash, etc.) / connect / be bound (by love, friendship, etc.) / enter a contract, form an alliance / wrap up, wind up / conclude, end

(colloquial) a girlfriend (a female partner in a romantic relationship)

(formal) Female third-person singular pronoun; she, her, girlfriend

past tense and perfective aspect of 結ぶ (musubu) [godan]

(literary) they (about women or girls)

to bear fruit

The bethrothed are to tie the knot. The newlyweds' fingers are bound together by a red rope, symbolizing that their destinies are now bound forever.