Half an Apple

Hikaru is a firm believer in fate--always describing soul mates as two halves of one apple--and she dreams of the day she will meet her true love.
One day Hikaru is reunited with a man, Shindou, whom she went to school with 10 years before, and believes fate has brought them back together.
Natsuko, one of Hikaru's co-workers, refuses to lose to Hikaru in love, and pulls out all the stops in order to capture the man she desires.
But who is the unsociable, austere stranger named Amano, and what part will he play in this exhilarating story of life and love?

(NOTICE: This series has some adult situations, but I don't know that it is enough to classify it as "adult" or "mature" or "smut". The situations are few, and on a reasonably classy level.)

(from mangaupdates)