The "Plus Are kara" (And After That) portion is a major selling point of this release. It functions as the "After Story." It takes place after the main route where the couple has solidified their feelings. It explores the difficulties of maintaining a secret relationship that turns into genuine love, dealing with workplace gossip, potential transfers, and the eventual proposal and life beyond the kitchen. It provides the "Sweet" conclusion that the "Unsweet" beginning promised.
"Unsweet Kurose Katsuko Plus Are Kara" appears to be a phrase combining Japanese words and names; interpreted literally: unsweet kurose katsuko plus are kara